To provide a key switch favorable to crime prevention without leaving a crime prevention device in an unwatching state even if the crime prevention device is placed in an unwatching state.

A crime prevention key switch is equipped with first and second sides, and it is constituted of a key switch main body having an insertion hole 5a of a key turned and energized to the first side and a contact SW3 closed when the insertion hole is turned to the second side. The crime prevention key switch is constituted of a watching/unwatching switching device R for switching a watching state and an unwatching state of a crime prevention device and a control section 6 for the watching/unwatching switching device R to set the crime prevention device in an unwatching state when the contact SW3 is closed and for the watching/unwatching switching device R to set the crime prevention device in a watching state after the elapse of delay time when the contact SW3 is opened.