A hand pushed lawn mower includes a power unit including a motor and a circuitboard, a support device for supporting the power unit, and a fan that rotatesabout a rotatingaxis. The power unit is detachably connected with the support device andincludes a powerunit housing. The power unit housing includes a containing chamber forcontaining themotor and the circuit board, an air inlet allowing an air flow to flow intothe containingchamber, and an air outlet allowing the air flow to flow out of the containingchamber.When the fan is rotated, the air flow which flows into the containing chamberfrom the airinlet at least passes in contact with the circuit board and then flows out ofthe containingchamber through the air outlet.
