PURPOSE: To prevent attaching of dust to a laser sensor by inclining a laser beam transmitting member of a dustproof cover so as to cross at a specified angle or less to an optical axis of the laser beam.

CONSTITUTION: A dustproof cover 10 with a sealed structure, which in the dustproof mechanism for preventing attaching of dust and waterdrops floating in the air is arranged in the surrounding of a laser sensor 1. The dustproof cover 10 is formed with a conical laser beam transmitting member 11 whose top is flat, and whose side wall surface is inclined at 10 degrees or more to the vertical direction. The side wall surface crosses at 80 degrees or less to the optical axis of a laser beam 9 so as not to make incident a regular reflection component of the laser beam 9 on a detector 8. The irregular reflection component of the laser beam 9 goes on a path different from an incident path of the laser beam 9 and erroneous recognition as reflecting light from an obstacle can be avoided.