PURPOSE:To remove efficiently a muddy film formed on an excavated wall surface of a continuous underground foundation. CONSTITUTION:A guide rail 25, which is formed in a part of a joint member buried on the side ends of a preceding element of a continuous underground foundation, and an engageable guide member 20 are installed to the side surfaces of the foundation and suspended with a hanging wire 39 from the ground. A support beam 30, which supports a brush 32, whose end is laid out so as to come in contact with a groove wall surface at the position of a joint between the elements of the continuous underground foundation, is fixed with a main frame 10, which may rise along a guide rail 25 by winding up and unwinding the hanging wire 39 in the groove where the continuous underground foundation is constructed. A muddy film formed on the groove wall surface is scraped and removed with the brush 32 which moves vertically by accompanying the lift motion of the main frame 10.