A rotation transmission device is mounted in a drive train of a four-wheel drive vehicle to selectively distribute driving force to selected vehicle wheels according to the travel condition of the vehicle. This device includes an outer ring and an input shaft. A cylindrical face is formed on one of the opposed surfaces of the outer ring and the input shaft, while cam faces are formed on the other opposed surface to define a wedge-shaped space between the cylindrical face and each cam face. Rollers are mounted in pockets formed in a retainer mounted between the input shaft and the outer ring. An electromagnetic clutch is coupled to the retainer. A switch spring is mounted between the retainer and the input shaft. A two-way clutch is provided between the outer ring and the input shaft. A control unit controls the two-way clutch by adjusting the amount of current fed through a coil of the electromagnetic clutch according to the travel condition of the vehicle, thus selectively distributing driving force to selected vehicle wheels. A method of controlling the rotation transmission device is also proposed. Also, another transmission device is proposed which is mounted in the transfer of a vehicle.