a frame unit;

a power unit mounted to the frame unit and including a flywheel that is rotatable;

a swing arm unit pivotably connected to the frame unit and including a conversion member, the swing arm unit being operable to swing relative to the flywheel in a first direction between an initial position, in which the swing arm unit and the flywheel have a maximum distance therebetween, and a triggered position, in which the swing arm unit and the flywheel have a minimum distance therebetween;

an impact unit adapted for striking a nail, movably mounted to the swing arm unit, and operable to be moved by the swing arm unit to come into contact with the flywheel, when the impact unit is in contact with the flywheel, the impact unit being urged by rotation of the flywheel to move in a nail-striking direction that is substantially orthogonal to the first direction; and

an actuation unit mounted to the frame unit and including a pushing member and an actuation member, the pushing member being rotatable relative to the frame unit and having a pushing surface that faces the conversion member, the actuation member including a pushing rod that is operable to move relative to the pushing member in the first direction between an extended position, in which the pushing member pushes the conversion member via the pushing surface thereof so that the swing arm unit is in the triggered position, and a retracted position, in which the swing arm unit is in the initial position.