BORING APPARATUS

PURPOSE: To provide a boring apparatus which is more compact in structure and smaller in the number of hoses than that of the conventional apparatus, by positioning the hitting part of a shank rod integrally provided with a large diameter hitting part and bar-like small diameter parts in an interspace between a front cylinder and a rear cylinder and arranging its small diameter parts at both sides along the shaft direction of a drifter body so as to fit to cylindrical hitting pistons at both sides. CONSTITUTION: In the case of applying a reverse hitting, when the drifter 1 is retreated, high pressure oil comes into a pilot valve device 45 for hitting from a port Pa. At this time, the pressure oil acts on a pilot Pd from a feed retreating circuit for retreating the drifter 1. When the pressure oil overcomes the pushing force of a spring 59, a valve 60 is changed over, and the pressure oil from the port Pa comes into a valve device 43 for reverse hitting after passing through a port Pi to operate a piston 33 for reverse hitting. At this time, returning oil is returned back to an oil tank from a port Pc through a port Ph from a port Pj.