A cam shaft phase setter including a control valve for controlling the feeding and draining of a hydraulic fluid into and out of a pressure chamber which serves to adjust the rotational angular position of a cam shaft relative to a crankshaft of an internal combustion engine. The control valve includes a valve housing with an operating port to the pressure chamber and a reservoir port to a reservoir for the fluid. A valve piston is axially adjustable back and forth in the valve housing between a first position and a second position and includes an axial hollow space, a piston inlet for introducing the fluid into the hollow space, and a piston outlet which leads out of the hollow space and is connected to the operating port in the first position of the valve piston and separated from the operating port in the second position of the valve piston. An actuating unit is coupled to the valve piston for axially adjusting the valve piston. A coupling member protrudes through an axially facing closure wall which closes off the valve housing and couples the actuating unit to the valve piston. The valve piston includes a radial widening which is surrounded by a complementarily widened housing portion of the valve housing and to which the fluid can be applied in an axial direction pointing away from the axially facing closure wall in order to generate an axial pressure force. The widening is dimensioned such that the fluid acts on the valve piston with a pressure force of at least substantially equal size in both axial directions, despite the coupling member.