To perform a surface treatment of a face to be treated efficiently without damaging a base of an object to be treated by colliding foaming plastic particle bodies against a surface of the object to be surface-treated to improve the quality of the surface thereof.

A plurality of foaming plastic particle bodies (plastic particle bodies) 1 are supplied to a shooting device 3 from a hopper 2. They are shooted continuously from a shooting mouth 3a toward a surface 4 of an external wall of a building which is coated, collide against the painted surface 4 of the external wall of the building, and are caught by a net 5 which is stretched radially from the shooting mouth 3a to the coated surface 4 of the external wall of the building after they collide against the surface 4 thereof. The plastic particle bodies 1 which are caught are transferred to a dust remover 6 to remove dust adhered on a surface of the plastic particle body 1 by the dust remover 6. Next, the plastic particle bodies 1 are transferred to a washer 7 and a dryer 8 sequentially so that dirt adhered on the surface of the plastic particle body 1 is removed by the washer 7 and the plastic particle body 1 from which dirt is removed is dried by the dryer 8.