The utility model provides a lawn mower which is provided with a height adjustment mechanism for adjusting the height of a trimming edge relative to the ground, preventing breaking, generated due to the fact that the trimming edge is inclined forwards and touches the ground, of the trimming edge and conducting simple height adjustment. The bottom of a shell of the height adjustment mechanism is provided with a sliding piece for sliding along the ground. The sliding piece is arranged on a supporting part at the rear end of the bottom of the shell in a supported mode, wherein the sliding piece can rotate around a horizontal axis which is orthogonal in the front-rear direction. A clamping part arranged on the front portion of the sliding piece is made to be selectively clamped with any one of clamping concave parts arranged on the front portion of the shell in the up-down direction so that the up-down position of the front portion of the sliding piece relative to the shell can be changed and the height position of the trimming edge relative to the ground can be changed. The supporting part is designed in the mode of capable of moving in the front-rear direction, and the supporting part is provided with a force applying part for applying force on the sliding piece in the direction in which the clamping part is clamped to the clamping concave parts.
