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