Abstract: A rock splitter of oil hydraulic piston type includes a housing having a plurality of cylinder chambers on the upper portion and first and second paths communicated with the cylinder chambers for supplying and discharging oil; a piston in the cylinder chamber of the housing; and a cap capable of a vertical movement, the cap being connected to the upper surface of the housing in such a manner that the inner surface thereof is in contact with the upper surface of the housing. The cap moves vertically depending on the movement of the piston. The rock splitter further comprises: a cylinder detachably mounted inside the cylinder chamber of the housing; a collapsible member having a locking member detachably mounted in the cylinder chamber, a plurality of extension members capable of a vertical extension; and an elastic member supporting the lower end of a central extension member. The entire front surface area of the cap touches the rock to maximize the power applied to the rock.