Abstract: The heretofore known adjusting device for an axial piston pump/motor of a tilting axis type in which a tilt angle of a valve plate is varied by rocking the valve plate along arcuate guide grooves formed in an end cover of the axial piston pump/motor is improved so as to reduce the size of the adjusting device in the direction of its stroke by assembling a sleeve or sleeves and a piston fitting in the sleeve or sleeves in a telescopic structure within a cylinder formed in the end cover along a rocking direction of the valve plate, and by providing a trunnion pin engaged with the valve plate in the piston.