To provide a crime prevention apparatus capable of automatically changing the volume of an alarm tone and a guide sound in accordance with a peripheral environment.

When the crime prevention apparatus 11 detects an intruder or the like by using a crime prevention sensor 14 (S12), an alarm volume set value is read out from a memory 19, and then the volume of an alarm tone is determined on the basis of the alarm volume set value and the alarm tone is output (S15). The output alarm tone is detected by using a microphone 17 and whether or not the detected alarm volume (alarm volume detection value) is within a allowable alarm volume range is checked (S17). When the alarm volume detection value exceeds the allowable range, a difference between the alarm volume set value and the alarm volume detection value is calculated and an alarm volume correction value is calculated (S18 to S20). Then the alarm volume set value is updated on the basis of the calculated alarm volume correction value (S21) to change (increase/decrease) the alarm volume.