To accurately wash out a belt 4 in a belt conveyor of a food processing machine in which a drive pulley 2 and a guide pulley 3 are disposed at an interval, the belt 4 is engaged with the drive pulley 2 and the guide pulley 3, and the belt 4 is driven by the drive pulley 2.

When the belt 4 is washed out, an arm 15 is unlocked by a lock mechanism, the arm 15 is swung about a pivot pin 14, the belt 4 is loosened by the arm 15, and the belt 4 is separated from the drive pulley 2 and the guide pulley 3.