A four-wheel-drive vehicle comprising: a drive source which generates torque forming a driving force of the vehicle; a driving force transmission system which transmits the torque of the drive source to main driven wheels (104L, 104R) and auxiliary driven wheels (105L, 105R); a dog clutch provided in the driving force transmission system and capable of transmitting the torque to an auxiliary driven wheel side by engagement of a recess portion and a protruding portion (31, 32); a determination unit (9b 1) which determines whether a friction coefficient of a road surface is lower than a predetermined value based on an index value relating to the friction coefficient of the road surface; and a control unit (9b 2) which generates a control signal which causes engagement of the dog clutch before the vehicle starts when the determination unit (9b 1) determines that the friction coefficient of the road surface is lower than the predetermined value, characterized by a control clutch provided on an upstream side or a downstream side of the dog clutch in the driving force transmission system as viewed in a torque transmitting direction and capable of controlling the torque transmitted to the auxiliary driven wheel side, wherein the control unit (9b 2) generates: a first control signal which causes engagement of the dog clutch before the vehicle starts when the determination unit (9b 1) determines that the friction coefficient of the road surface is lower than the predetermined value; and a second control signal which instructs the control clutch to increase the torque transmitted to the auxiliary driven wheel side when the main driven wheels (104L, 104R) slip at the start of the vehicle, wherein the control clutch has an electromagnetic coil, and when the four wheel drive vehicle is shifted from a two-wheel drive to a four-wheel drive, a gradually increased current is supplied to the electromagnetic coil, the control clutch is rotationally driven by the rear wheels (105L, 105R), a propeller shaft is rotated by the control clutch, first and second rotational speeds upstream and downstream of the dog clutch viewed in torque transmission direction are detected by first and second speed detectors (91, 92), respectively, wherein the synchronization is based on the difference of the detected rotational speeds, and thereafter the dog clutch is engaged. a drive source which generates torque forming a driving force of the vehicle; a driving force transmission system which transmits the torque of the drive source to main driven wheels (104L, 104R) and auxiliary driven wheels (105L, 105R); a dog clutch provided in the driving force transmission system and capable of transmitting the torque to an auxiliary driven wheel side by engagement of a recess portion and a protruding portion (31, 32); a determination unit (9b 1) which determines whether a friction coefficient of a road surface is lower than a predetermined value based on an index value relating to the friction coefficient of the road surface; and a control unit (9b 2) which generates a control signal which causes engagement of the dog clutch before the vehicle starts when the determination unit (9b 1) determines that the friction coefficient of the road surface is lower than the predetermined value,