To prevent a collision between an automobile moving out and a car washing machine, and obtain a safer car washing machine in a drive-through portal car washing machine.

In the portal car washing machine, a detecting means 21 constituted of a reflective type laser sensor detecting the automobile A moving out on the rear end part of a car washing machine body 1, and a moving means in a light projecting/receiving direction for enlarging the detection range of an object by the reflective type laser sensor are provided. When the car washing machine body is retreated to a car washing starting position after the car washing is finished, the retreat of the car washing machine body is stopped on the detection of the object by the detecting means.