What is claimed is:1. A deadman switch mechanism for an emergency stop of a robot, comprising:a plurality of switches each having an ON-state and an OFF-state;switching means for switching said plurality of switches between the ON-state and the OFF-state; andmeans for outputting a signal for allowing a robot to operate on the condition that all of said plurality of switches are in the ON-state,wherein said switching means includes at least one handling member having an external-operating-force receiving portion exposed outside, a handling-member supporting member for supporting said at least one handling member so that said at least one handling member moves in accordance with an external operating force applied to said external-operating-force receiving portion, and a switch turning member linked with all of said at least one handling member, for simultaneously turning said plurality of switches to the ON state/the OFF-state.2. A deadman switch mechanism for an emergency stop of a robot according to claim 1, wherein a plurality of handling members are provided as said at least one handling member.3. A deadman switch mechanism for an emergency stop of a robot according to claim 1, said switch turning means is a linkage mechanism linked with all of said at least one handling member.4. A teaching operation panel having a deadman switch mechanism for an emergency stop of a robot,said deadman switch mechanism for an emergency stop of a robot comprising: a plurality of switches each having an ON-state and an OFF-state; switching means for switching said plurality of switches between an ON-state and an OFF-state; and means for outputting a signal to allow a robot to operate on the condition that all of said plurality of switches are in the ON-state,wherein said switching means includes at least one handling member having an external-operating-force receiving portion exposed outside, a handling-member supporting member for supporting said at least one handling member so that said at least one handling member moves in accordance with an external operating force applied to said external-operating-force receiving portion, and a switch turning member linked with all of said at least one handling member, for simultaneously turning said plurality of switches to the ON-state/the OFF-state.5. A deadman switch mechanism for an emergency stop of a robot according to claim 4, wherein a plurality of handling members are provided as said at least one handling member.6. A deadman switch mechanism for an emergency stop of a robot according to claim 5, wherein the external-operating-force receiving portions of said plurality of handling members are exposed outside a case of said teaching operation panel at separate positions.7. A teaching operation panel according to claim 6, wherein said plurality of handling members comprises two handling members arranged on the left and the right of said teaching operation panel, respectively, and the force application portions of said handling members are exposed outside the case of said teaching operation panel on the left and the right thereof.8. A deadman switch mechanism for an emergency stop of a robot, comprising:a plurality of switches each being switched between an ON-state and an OFF-state;swiching means for simultaneously switching all of said plurality of switches from the ON-state to the OFF-state, or from the OFF-state to the ON-state in response to an operating force from an operator; andmeans for outputting a signal for allowing a robot to operate on the condition that all of said plurality of switches are in the ON-state.9. A deadman switch mechanism according to claim 8, wherein said switching means includes a plurality of turning members respectively provided for said plurality of switches and to operate directly on said plurality of switches, a link member for mechanically linking said turning members, and at least one handling member for receiving the operating force from the operator and transmitting said operating force to said link member.