To provide a means for eliminating a clearance conventionally generated when closing a closing member, and making further surely evadable harmful organisms without impairing smoothness of opening-closing the closing member such as a shutter, and without compelling labor for opening-closing the doorway.

This clearance blocking mechanism of a building opening-closing part closes clearance between an opening part of a building such as the doorway and a window and the closing member such as a door and the shutter for closing the opening part. This clearance blocking mechanism of the building opening-closing part has a fixing base body 1 and a brush part 2 arranged in the fixing base body 1, and the brush part 2 covers the clearance between the closed opening part and the closing member by fixing the fixing base body 1 to the opening part or the closing member. The brush part 2 contains a repellent of the harmful organism such as an insecticide.