An electric motor-attached speed reducer includes a first member, an electric motor, a speed reduction mechanism, and a second member. The electric motor is arranged to produce rotational motion with respect to the first member. The speed reduction mechanism is arranged to transfer the rotational motion obtained from the electric motor while reducing the speed thereof. The second member is arranged to rotate relative to the first member at a rotation rate resulting from the speed reduction. A first bearing is arranged between the first and second members. A second bearing is arranged between the first member and a rotor of the electric motor. The speed reduction mechanism includes a flexible third bearing arranged between a non-perfect circular cam and a flexible external gear. The second bearing is arranged to radially overlap with a rotor holder at a first axial position. The third bearing is arranged to radially overlap with the rotor holder at a second axial position different from the first axial position.