PURPOSE: To prevent a temperature rise in a main body by cooling cut dust to be collected into a dust collecting chamber.

CONSTITUTION: In an upper part of a circular saw device main body, an outer wall 40 is provided in the rear side of a gear housing 3 extendedly from a motor housing 2 to the gear housing 3 while plural oblong holes 42, 42... are pierced in a left corner of the upper part of the main body in an inner wall 41 of the gear housing 3. In this constitution, an air duct, in which one part, of an air flow of a motor cooling fan 6 is delivered to a dust collecting chamber 16 side through between the outer wall 40 and the gear housing 3, is formed. Therefore, cut dust to be collected into the inside of the dust collecting chamber 16 is always cooled down by an air flow A while the circular saw device main body is cooled down according to cooling down of wall parts of a dust cover 4, a blade cover 15, and the like, so that the temperature rise in the dust collecting chamber is prevented even though high temperature cut dust is collected when a material to be cut is metal material.