A vehicle door opening/closing actuator includes a tubular housing, a motor part accommodated in the housing, a feeding apparatus accommodated in the housing and that supplies power to the motor part, and a closed-bottom tubular seal section that has a circumferential wall arranged to be interposed between an inner circumferential surface of the housing and an outer circumferential surface of the feeding apparatus, and that is arranged to cover the feeding apparatus with an entire thereof, wherein a rib extending in a circumferential direction is formed at an inner circumferential surface of the circumferential wall of the seal section, and a concave section that receives the rib is formed at the outer circumferential surface of the feeding apparatus.