In the wave gear unit (1), the input shaft (2) is positioned in the direction of the central axis (1a) by first and second input bearings (3, 4). A first unit end plate (5) on the first input bearing side is a compound member in which a bearing housing member (22) obtained from a ferrous material is integrated with a main end plate body member (21) obtained from a lightweight material. A second unit end plate (6) on the second input bearing side is integrated with a rigid internal gear (13), the unit being a compound member in which a second member (26) obtained from a lightweight material is integrated with a first member (25) obtained from a lightweight material. The first member (25) is provided with a main end plate body section (25a) of the second unit end plate (6) and a main gear body section (25b) of the rigid internal gear (13). The second member (26) is provided with a bearing housing section (26a) of the second unit end plate (6) and a teeth-forming section (26b) of the rigid internal gear (13). A lightweight wave gear unit is achieved.