PROBLEM TO BE SOLVED: To correctly execute the angle of turnabout and to reliably clean a swimming pool of a desired shape. SOLUTION: A cleaner 2 that can travel forward and backward in a swimming pool 1 has a driving mechanism that can switch between forward travel and backward travel, and one motor is provided on the left side of the driving mechanism and the other one on the right side. In addition, a controlling device tat controls the driving mechanism is provided. The controlling device has a speed regulator for each part of the driving mechanism, and in addition, has a means for performing differential control of the speeds of two motors. The cleaner has a means to measure forward and backward travel distances d1 and d2 on both sides. Based on the measured forward and backward travel distances d1 and d2 and offset width (v) of each course of movement, the controlling device calculates the angles of turnabout R1 and R2 for differential control.