A liquid sealed vibration isolating device is integrally provided with an elastic movable diaphragm and a relief valve. A pair of parallel straight line sections is on opposite sides of a circular elastic partition member. The elastic movable diaphragm includes a center of the elastic partition member and is surrounded by a pair of opposed circular arc sections and a pair of straight line sections formed by cutting an outer circumferential part of the elastic partition member. The relief valve is radially outward of the straight line section of the elastic partition member. A part of the elastic movable diaphragm reaches the circular arc section corresponding to the outer circumferential part of the elastic partition member so as to be increased in area as much as possible to absorb an internal pressure of a primary liquid chamber and to achieve low dynamic spring.