The present invention is concerned with an apparatus for controlling a straight excavating operation with a hydraulic excavator such as a power shovel or the like machine including three working units, i.e., a boom, an arm and a bucket. When the straight excavating operation is performed, a hydraulic pressure of hydraulic oil in a hydraulic chamber on the boom lowering side of a boom cylinder is conducted to a drain tank while maintaining a predetermined set pressure, and a hydraulic pressure of hydraulic oil in a hydraulic chamber on the boom raising side of the boom cylinder is conducted to the drain tank via a check valve which serves to inhibit the hydraulic oil from flowing from the hydraulic chamber on the boom raising side of the boom cylinder to the drain tank, whereby the boom is held in the so-called floated state so as to enable a straight excavating operation to be performed merely by actuating the arm and bucket. In addition, according to the present invention, the apparatus is provided with an automatic bucket driving system for automatically controlling the present bucket angle so as to coincide with a preset bucket angle. This system contributes to remarkable reduction of a load to be borne by an operator while a straight excavating operation is performed.