To enable one operator to execute the automatic washing of a panel, by transporting a construction panel by a transporter in a plane direction, turning a rotary brush which is made to touch a panel while turning, and jetting a detergent.

A construction panel P is transported in the plane direction of the panel P with a transporter 3, a rotary brush 4 is made to touch the panel P while turning. And then, the panel P is washed by driving the rotary brush 4 with a brush driver 5 and jetting a detergent to the panel P from a detergent injector 8. And then the panel P is dried by supplying drying wind to the panel P from a drier 9. It is desirable that a waiting section 2 on which a panel P to be delivered to the transporter 3 and/or one discharged from the transporter 3 are placed is provided in one or both of the transport directions of the transporter 3.