Support arms are disposed on a tilting shaft on a bracket of an outboard motor. An electric actuator is mounted between the support arms. The electric actuator includes a cover member, first and second electric motors disposed individually on the opposite ends of the cover member, a feed screw configured to be rotated by the electric motors, a nut member configured to move along an axis as the feed screw rotates, a drive arm configured to move integrally with the nut member and transversely relative to the boat body, and protective boots. The drive arm is connected to a steering arm through an engaging member. If the drive arm moves in the direction of the axis along the cover member, the steering angle of the steering arm changes depending on the degree of movement of the drive arm.