A viscous fluid-sealed damper (1) having a shaft receiving section (2c) in which an installation shaft (3) with a swollen head (3b) is fitted and also having a separation wall (2). At least a portion of the separation wall (2) is constructed from an elastic separation membrane, and the separation wall (2) continues to the periphery of the upper edge of the shaft receiving section (2c) such that the shaft receiving section (2c) extends inward. Viscous fluid is sealed inside the separation wall (2). A positioning section (2f) for positioning the shaft receiving section (2c) is provided at that position of a bottom face (2a) of the separation wall section (2) that faces the shaft receiving section (2c). The viscous fluid-sealed damper can be assembled with good work efficiency and is unlikely to be damaged during assembly.