A blade replacement apparatus of an electric instrument is provided. The blade replacement apparatus includes a nut, a nut loosening/tightening member, a locking member, and an operating member. One of the nut loosening/tightening member and the operating member has a first matching portion, the locking member having a second matching portion. The operating member is movable between an operating position and a non-operating position. When the operating member is in the non-operating position, the first matching portion engages with the second matching portion, and the rotation of the nut loosening/tightening member is obstructed by the locking member. When the operating member is in the operating position, the first matching portion is disengaged from the second matching portion, and the rotation of the nut loosening/tightening member tightens or loosens the nut.