Abstract: A scroll type fluid displacement apparatus, in particular, a scroll type compressor, is disclosed. The apparatus includes a pair of scroll members at an angular and radial offset for forming fluid pockets, each scroll member having a spiral element. A bypass hole is provided on a wall of at least one of the spiral elements of the scroll members for communicating between the fluid pockets and a suction chamber. A valve mechanism, which operates in a radial direction, controls the opening and closing of the bypass hole. The valve mechanism is responsive to the rotational motion of the scroll members and/or the pressure in at least one of the fluid pockets. When the apparatus is driven at excessive speed, the valve mechanism operates in response to centrifugal force to open the bypass hole. The compressed fluid in the fluid pockets then is released into the suction chamber through the opened bypass hole, and the compression capacity is reduced to a proper value.