PURPOSE: To provide a power-off monitor device which quickly discriminates the factor of power-off and extends the time when the power-off interrupt handling is possible.

CONSTITUTION: The latency time to convergence of chattering of a power switch 2 is not provided, and the state of the power switch 2 is held in a switch state holding circuit 4 by a pulse exceeding a prescribed threshold value. A main power-off detecting circuit 3 discriminates the state of the switch state holding circuit 4 just after detecting power-off of a main power source 1. When it is discriminated that the switch is turned on, the first power-off interrupt handling is performed; and when it is discriminated that the switch is turned off, the second power-off interrupt handling is performed.