| 摘要 |
A worm speed reducer (17) includes a worm wheel (19) that has an outer peripheral surface (43) having a tooth portion (19c) formed therein, a worm shaft (18), and a biasing member (60). The worm shaft (18) has a meshing portion (18d) that meshes with the tooth portion (19c) between a first end (18a) located adjacent to the electric motor (16) and a second end (18b) located on the opposite side. The distance (L2) between the meshing center (B) and the second end (18b) is larger than the distance (L1) between the meshing center (B) and the first end (18a). The biasing member (60) biases the second end (18b) by use of the first end (18a) serving as a fulcrum. |
