A liquid ring vibration control device, wherein an idle orifice passage (17) is provided in a partition member (12) separating a main liquid chamber (13) from an auxiliary liquid chamber (14), the opening (18) thereof is opened and closed by a seating part (20) provided at a part of a diaphragm (15), and the opening and closing are controlled by a pressing member (21), the seating part (20) is formed in thick wall and recessed parts (51, 52) are provided in the center part front and rear surfaces of the diaphragm so as to form a thin−walled part (53), a generally semi−spherical projection (54) and a seal (55) of generally right triangle in cross section are installed around the seating part (20), a lateral film part (10) is installed on the side surface of an elastic body part (3), the outer peripheral part of the partition member (12) is floatingly supported through a cushion flange (33) and an elastic peripheral wall (37), and the upper end of a coiled spring (48) is floatingly supported by a pressing part (41) formed with an elastic material.
