PURPOSE: To obtain the input device which can accurately detect the states of a two-key roll-over type keyboard consisting of plural movable contactors and a specification setting switch for the device with simple and inexpensive constitution.

CONSTITUTION: A common strobe signal 2 generated by a strobe signal generating circuit 22 is used as a strobe signal for retrieving the operation state of the movable contactors of the two-key roll-over type keyboard 4, arranged in a matrix shape, and a strobe signal for retrieving the setting state of the specification setting switch 5 so as to read the input and setting states of the keyboard 4 and specification setting switch 5. A key data read circuit 23 decides whether or not the setting state of the specification setting switch is correct according to the combination of keys which are depressed at the same time, and inputs the state of the specification setting switch again when the detection result is not correct or matches it with contents read in the last retrieval cycle when correct.