The dust proof circular saw has a main body with a rotating disc cutter blade and a cover fixed to the body to cover a blade outer radial periphery part. The body is supported by a base such that an angle of the body in the up-down and right-left directions can be adjusted at a base upper side. A further blade outer radial periphery is covered by an auxiliary cover. The auxiliary cover covers a gap between the fixed cover and the base. The auxiliary cover is moved by a mechanism relative to the body in accordance with an angle of the circular saw main body relative to the base in the up-down direction. The auxiliary cover is pivotally connected to the base, and is pivoted around a laterally tilting support shaft in the right-left direction by an interlock mechanism in accordance with a body angle in the right-left direction.