An infinitely variable transmission in which the pitches of a driving pulley and a driven pulley are variable by means of hydraulic fluid pressure to vary the velocity ratio between the two pulleys. A lower pressure fluid and a higher pressure fluid are created from a hydraulic fluid from a hydraulic fluid supply source, with a constant pressure difference therebetween. The lower pressure fluid has its pressure value varied in response to the velocity ratio. The lower pressure fluid and the higher pressure fluid are selectively supplied to the movable pulley elements of the driving pulley and driven pulley. A hydraulic clutch and a pressure regulating valve are connected together by a hydraulic fluid supply passageway which is selectively closed and opened by a supply control valve. A drain passage is connected to the hydraulic fluid supply passageway to allow hydraulic fluid to escape from the hydraulic clutch when the passageway is closed by the supply control valve. In at least one movable pulley element, an orifice is formed through a sealing element which seals between an inner peripheral surface of a cylindrical portion and a radially extending annular flange of a stationary piston element to communicate between first and second hydraulic pressure chambers defined within an annular space in a pulley main body at opposite sides of the annular flange of the stationary piston element.