A walk-behind lawnmower having a height adjusting mechanism for adjusting the height of a housing above the ground. The height adjusting mechanism includes: a front wheel supporting member and a rear wheel supporting member that are attached to the housing so as to be capable of swinging up and down; a linking member for linking the front and rear wheel supporting members so as to be capable of concerted motion; and a locking mechanism for restricting and releasing displacement of the linking member in the forward-and-backward direction. The locking mechanism includes: a plurality of locking grooves arranged in a row from front to rear on the linking member; a locking pin capable of selectively interlocking with one of the locking grooves; a pin-guiding part for guiding the locking pin to be capable of entering into and retracting from one of the locking grooves; and an operating member for sliding and operating the locking pin.