To provide a closing device with a deceleration mechanism for a door with improved design in a thin and long compact shape, for which a pull-in mechanism is provided in both of a body device and a receiving device in the configuration of separating the body device and the receiving device at a prescribed angle position and braking only a connected range.

The closing device with the deceleration mechanism for a door includes a body case provided with an atypical oblong hole, a horizontal slide member, a moving bearing provided with a bearing recessed part, a deceleration member and a spring for pull-in. The moving bearing is rotatably arranged to the horizontal slide member, the deceleration member is inserted together with both of them into the body case, the spring for pull-in is energized between the horizontal slide member and the body case, and the body device is constituted. Also, a swing arm provided with an upper shaft is freely turnably mounted on a receiving case, a spring for an arm is energized, and the receiving device is constituted. In the range that both devices are connected in door opening/closing operations, the upper shaft is moved inside the atypical oblong hole, and a deceleration operation is obtained together with a pull-in operation in linkage with the moving operation of the horizontal slide member and a deceleration device.