A four-wheel-drive vehicle comprising: a drive source that generates driving force for a vehicle; a first driving force transmission system that transmits the driving force to main drive wheels (104R, 104L); a second driving force transmission system that transmits the driving force to auxiliary drive wheels (105R, 105L); an operation receiving device that receives a starting operation for starting the drive source; and a control device that controls the second driving force transmission system, wherein the second driving force transmission system includes a dog clutch that transmits the driving force when a recessed portion and a projected portion (31a, 32a) of the dog clutch are engaged with each other, and a driving force transmission device that is able to continuously adjust the driving force to be transmitted, and wherein the control device includes a road surface state determination section that determines whether a coefficient of friction of a road surface is equal to or higher than a predetermined value based on an index value regarding the coefficient of friction of the road surface, characterized in that the control device is configured to control the dog clutch such that the recessed portion and the projected portion are engaged each other irrespective of the index value regarding the coefficient of friction of the road surface when the operation receiving device receives the starting operation, and is configured to control the dog clutch such that engagement between the recessed portion and the projected portion is cancelled when the road surface state determination section determines that the coefficient of friction of the road surface is equal to or higher than the predetermined value. a drive source that generates driving force for a vehicle; a first driving force transmission system that transmits the driving force to main drive wheels (104R, 104L); a second driving force transmission system that transmits the driving force to auxiliary drive wheels (105R, 105L); an operation receiving device that receives a starting operation for starting the drive source; and a control device that controls the second driving force transmission system, wherein the second driving force transmission system includes a dog clutch that transmits the driving force when a recessed portion and a projected portion (31a, 32a) of the dog clutch are engaged with each other, and a driving force transmission device that is able to continuously adjust the driving force to be transmitted, and wherein the control device includes a road surface state determination section that determines whether a coefficient of friction of a road surface is equal to or higher than a predetermined value based on an index value regarding the coefficient of friction of the road surface, characterized in that the control device is configured to control the dog clutch such that the recessed portion and the projected portion are engaged each other irrespective of the index value regarding the coefficient of friction of the road surface when the operation receiving device receives the starting operation, and is configured to control the dog clutch such that engagement between the recessed portion and the projected portion is cancelled when the road surface state determination section determines that the coefficient of friction of the road surface is equal to or higher than the predetermined value.