The construction machine includes a floor plate, a seat and a control box provided on the floor plate, a support plate having an end portion, in a left-right direction, configuring a supporting end portion, on which the control box is mounted, a second slide rail that extends in a front-rear direction and is attached to a lower surface side of the support plate, and a reinforcing block that extends in a direction crossing the second slide rail in a plan view. The reinforcing block has a portion extending toward an end surface of a supporting end portion from a position in an area of the second slide rail in a plan view, and the portion being attached to the supporting end portion of the support plate.