Abstract: An outer peripheral surface of a cam has an apex disposed of distance from a rotational axis, a first region adjacent the apex opposite to the direction of rotation that increases in distance from the rotational axis during rotation, and a second region adjacent the apex in the rotational direction that decreases in distance from the rotational axis of the cam with the rotation thereof. The apex is disposed where the phase ? thereof advances by 15 degrees and 55 degrees or less in the rotational direction from a position symmetrical to the rotational axis. The rate of change between the second region and the rotational axis is greater than the rate of change between the first region and the rotational axis. A retreat amount X when a saw blade reaches an uppermost point c from a foremost point is set to 0.8 mm.

Abstract: An outer peripheral surface of a cam has an apex having a greatest distance from a rotational axis, a first region located on the side of the apex opposite to the direction of rotation and having an increasing distance from the rotational axis with the rotation thereof, and a second region located on the side of the apex in the rotational direction and having a decreasing distance from the rotational axis of the cam with the rotation thereof. The apex is disposed in a position where the phase 0 thereof advances by 15 degrees or more and 55 degrees or less in the rotational direction from a position symmetrical to a center of the pin with respect to the rotational axis. The rate of change in the distance between the second region and the rotational axis is set to be greater than the rate of change in the distance between the first region and the rotational axis. A retreat amount X when a saw blade reaches an uppermost point c from a foremost point is set to be 0.8 mm or more at a lower end of the saw blade.