An antitheft apparatus includes a control section. When a status change from a closed state to an open state of a luggage door caused by regular means is detected in an arming state being ready to output an alarm, the control section shifts a status from the arming state to a disarmed state being not ready to output an alarm; when a status change from the open state to the closed state of the luggage door is detected in the disarmed state, the control section shifts the status from the disarmed state to the arming state after a predetermined length of preparatory period; and when an arming command to shift the status from the disarmed state to the arming state is given within the length of preparatory period, the control section shifts the status from the disarmed state to the arming state.