To provide a crime prevention system provided with at least an outer door and an inner door to prevent the inner door from being easily opened if the outer door is not normally opened and open the inner door easily if the outer door is normally opened.

This crime prevention system is provided with an outer door unlocking detection means, an outer door opening and closing detection means 61, a control means for receiving signals from these detection means to control a condition, and an inner door locking mechanism for switching locking/unlocking conditions of the inner door. The inner door locking mechanism is usually in an unlocked condition and receives an unlocking signal from the outer door unlocking detection means by the control means. When the outer door is normally opened and an opening signal from the outer door opening and closing detection means is received by the control means, an unlocking condition by the inner door locking mechanism is maintained to open the inner door. When the outer door is illegally opened without receiving an unlocking signal from the outer door unlocking detection means by the control means, the inner door locking mechanism is switched into a locked condition to prevent the inner door from being opened.