A four wheel drive motor vehicle is of a type which has a variable torque transfer through which the driving force distribution between front and rear wheels is varied in accordance with the magnitude of a fluid pressure supplied to the transfer. A fluid pressure control device for producing the fluid pressure comprises a first hydraulic circuit which is arranged to have a first operation mode wherein the first hydraulic circuit outputs, for the transfer, a fluid pressure which is varied continuously; a second hydraulic circuit which is arranged to have a second operation mode wherein the second hydraulic circuit outputs, for the transfer, a fluid pressure which is varied stepwisely; a piping for connecting the first and second hydraulic circuits to constitute a united hydraulic circuit; and shutters arranged in given portions of the piping to selectively open and close the given portions for allowing the united hydraulic circuit to have the first and second operation modes selectively.