An emergency-stop device provided in a robot system, a machine tool or the like, arranged to promptly detect failure of a circuit through which an emergency stop signal is supplied to an CPU, without stopping the robot system, the machine tool or the like, to improve reliability. When at least one of emergency stop switches is opened, a CPU #1 or #2 issues an emergency stop command through one of input circuits, so that a switch SW10 or SW20 is opened by an output circuit #1 or #2 to emergency-stop the system. Switching means #1, #2 are opened separately, at appropriate intervals, and change of output of each photo coupler is recognized. In this manner, it is checked that open/closed-state outputs related to contacts C11 and C21/C12 and C22, each connected to one of the input circuits, indicate an open state. If regarding any of the contacts, change of output of the corresponding photo coupler is not recognized, the system is stopped and an action such as causing a buzzer and displaying of an alarm is taken.