To provide a safe and efficient car washing machine washing as many of washable parts as possible in such a way that if there are protruding objects such as mirrors at the front and rear ends of an automobile body, the machine detects the positions of the objects along the cross direction of the automobile to avoid only the protruding objects.

This portal car washing machine 1, having car washing process devices such as washing brushes 8 and 9 and drying nozzles 12 and 13, is provided with a travel position detection means such as a rotary encoder for detecting the position of the car washing machine, a horizontal optical axis formed by arranging light projecting and receiving elements at the sides of the car washing machine body, and a diagonal optical axis formed by arranging light projecting and receiving elements on the top and the right and left sides of the car washing machine body. The automobile is washed by controlling the car washing process devices, according to the position of the car washing machine body or the automobile detected by the rotary encoder and the light transmitting or blocking states of both optical axes.