A base for an injection molding machine has two side frames extending parallel with the axis of a drive actuator. Each of the side frames includes a lower flange supported by a bed, an upper flange disposed parallel with the lower flange, at least two webs connecting the upper flange and the lower flange, and a web reinforcing member fixed to the webs and penetrating through the webs. The side frames each have stiffeners connected between the lower and upper flanges and to one of the webs.