A hydraulic excavator capable of achieving suppression of decrease in weight of a counterweight and appropriate arrangement of an exhaust gas treatment device is provided. A rear leg portion forming a leg portion supporting the exhaust gas treatment device against the revolving frame has a main body portion formed to have a U-shaped cross-section, and an open side of the U-shape of the main body portion is opposed to a counterweight. The counterweight has a pair of groove-shaped recesses formed, in which a pair of end portions of the U-shape of the main body portion is inserted.