To provide a keyless opening/closing system of a door by which appropriate measures can be taken according to the situation even when the door is unlocked despite the intention of the user, and security can be improved.

The keyless opening/closing system of the door comprises a portable transmitter 1 transmitting signals of an instruction code instructing locking/unlocking of the door, a receiver 8 having a lock control means outputting control signals for locking/unlocking the door according to the received instruction code, and a door lock opening/closing mechanism for locking/unlocking the door by receiving the control signals. The keyless opening/closing system is provided with a horn 19 emitting an alarm, and an alarm emission controlling means controlling the horn 19 to emit the alarm when the receiver 8 receives the signal for instruction of unlocking of the door under the unlocked state of the door.