Disclosed is a construction machine which comprises an engine (11), a fuel tank (14), and a liquid reductant tank (25) for storing a liquid reductant for purifying exhaust gas from the engine (11), allowing the liquid reductant tank (25) to be provided at a desired position without a significant increase in cost and required space, while suppressing a reduction in capacity of the fuel tank (14). The construction machine further comprises a tank cover (23), and the fuel tank (14) has an upper surface including a high-position surface (14b) and a low-position surface (14c) located at a lower position than the high-position surface (14b) and adjacent to the high-position surface (14b) through a step (14a). The tank cover (23) is provided over the low-position surface (14c) and at a height position approximately equal to that of the high-position surface (14b) to define a liquid reductant tank installation space (S) in cooperation with the low-position surface (14c). The liquid reductant tank (22) has a replenishment port (22a), installed in the liquid reductant tank installation space (S) so that the replenishment port (22a) is close to a lower surface of the tank cover (23).