A hand pushed lawn mower includes a power unit including a motor and a circuit board, a support device for supporting the power unit, and a fan that rotates about a rotating axis. The power unit is detachably connected with the support device and includes a power unit housing. The power unit housing includes a containing chamber for containing the motor and the circuit board, an air inlet allowing an air flow to flow into the containing chamber, and an air outlet allowing the air flow to flow out of the containing chamber. When the fan is rotated, the air flow which flows into the containing chamber from the air inlet at least passes in contact with the circuit board and then flows out of the containing chamber through the air outlet.
