A speed reducer-equipped motor includes a motor, first gear, eccentric shaft, and stopper protrusions. The speed reducer-equipped motor also includes a transmission gear, an output member, a rotation stopper, and an interference avoider. The transmission gear revolves around an axis of the first gear following rotation of the first gear along with the eccentric shaft. The output member rotates following the revolution of the transmission gear. The rotation stopper works to stop the transmission gear from rotating the center thereof in response to sliding motion of the stopper protrusions on the rotation stopper. The interference avoider is arranged between the rotation stopper and the transmission gear and works to avoid physical or mechanical interference of corners of the rotation stopper which are located close to the stopper protrusions with base end portions of the stopper protrusions.