A basic module 2 has operation program storing part for prescribing the relation between the state of a safety input signal to be fetched from external input terminal sections 32, 33 and the state of a safety output signal to be transmitted to external output terminal sections 41, 42 for each type of predetermined safety switches, type-of-switch setting part for setting external input terminal sections 31, 32 and the type of safety switches to be connected to the external input terminal sections, and operation program executing part for selecting a safety operation program corresponding to the type of the switch set by the setting part among a plurality of types of safety operation programs stored in the operation program storing part and executing the selected program for the external input terminal sections 31, 32 set by the setting part.
