A post-treatment device mounting frame on which an exhaust gas post-treatment device is mounted is constituted by a front mounting leg, a rear mounting leg, and a deck connecting the front and rear mounting legs to each other. A vertical leg part of the front mounting leg is mounted on a front vertical leg part mounting plate of a right front extension beam. A lateral leg part of the front mounting leg is mounted on a front lateral leg part mounting plate of a right front engine support bracket. A vertical leg part of the rear mounting leg is mounted on a rear vertical leg part mounting plate of a right rear extension beam. A lateral leg part of the rear mounting leg is mounted on a rear lateral leg part mounting plate of a right rear engine support bracket. Therefore, the post-treatment device mounting frame is firmly mounted in a state of four-point support on a revolving frame.