A control valve block (24) is mounted on a bottom plate (6A) of a revolving frame (6) through a control valve block mounting plate (18). In this case, a left support member (19) and a right support member (20) are provided on a back surface (18B) of the control valve block mounting plate (18) at two spots with equal distances sandwiching a center position of gravity (G) of the control valve block (24). The left and right support members (19, 20) are mounted on a support beam (8) provided on the bottom plate (6A) of the revolving frame (6). On the other hand, a weight-reducing part (7) is provided at a part in the bottom plate (6A) of the revolving frame (6) away from the support beam (8). The control valve block (24) which is a heavy article is stably supported on the bottom plate (6A) at two spots sandwiching its center position of gravity (G). Moreover, the weight of the revolving frame (6) can be reduced by the weight-reducing part (7).
