A connecting device 1 of a towing vehicle 2 includes a connecting pin 13, a locking arm 22, and an actuator 23. The connecting pin 13 is provided to be rotatable between a connection position where the connecting pin 13 is brought into fitting engagement with a connecting plate 3a of a wheeled platform 3 and a disconnection position where the connecting pin 13 is taken out of the fitting engagement with the connecting plate 3a. The locking arm 22 is driven by the actuator 23 between a locking position where locking arm 22 is locked with the connecting pin 13 such that the connecting pin 13 cannot rotate out of the connection position toward the disconnection position and an unlocking position where the connecting pin 13 is unlocked in the connection position.