PURPOSE: To offer a self-diagnosing device if an inputting circuit, which is capable of detecting not only disconnecting and a short circuit accident in a printed circuit substrate but also a disconnection accident and contact failure, etc. in a wiring part.

CONSTITUTION: In the figure, S5WS8 denote normal closed type input switches, and S8 denotes and input electronic switch of a transistor, etc., conducting at the time of non-operation or a normal state. In case of a diagnosing mode of a device to be controlled, at first, an output command IS of an output control part 4 is set to "0" (low level). In this case, unless any operation is executed to the input switches S5WS8, they are all on, therefore, each terminal t5Wt8 of an input control part 5 obtains a signal corresponding to an on-state of each intput switch. Accordingly, by storing a signal induced in the terminals t5Wt8, in a designated address of an RAM3, and inspecting it, it is possible to diagnose a disconnection accident, contact failure, etc. in a printed circuit substrate part B and a wiring part C.