To equip a chain saw with a danger-detecting sensor, which detects a person in a danger zone in which trees fall down, to detect a workman who is still in the danger zone and warn him or her to move out of the danger zone even when felling a standing tree while moving from one place to another on an irregular slope in a secluded place in the mountains.

A chain saw equipped with a danger-detecting sensor is provided with; a chain saw 2 which is equipped with a sensor 1 which detects a workman S who is still in a danger zone DZ; an interface which transmits and receives output signals which are obtained when the sensor 1 detects the workman S; and a warning tool 3 which warns the workman S in the danger zone DZ when the sensor 1 detects the workman S.