To prevent a differential lock status during operation, in a differential gear with a differential lock. A locking piece which rotates along with rotation of a differential case is attached to the differential case. A contact piece contactable with the locking piece is formed in a fork member that moves a lock pin to set the differential lock status. When the number of revolutions of the differential case becomes a predetermined number of revolutions, the locking piece moves to a position facing the contact piece, to regulate actuation of the fork member. Accordingly, the differential mechanism section is prevented from entry into the differential lock status.