The invention discloses an inner hole machining device. The device comprises a horizontally placed base, wherein a vertically-arranged rectangular positioning plate is arranged on the base; a clamping plate is arranged on the base; the clamping plate is positioned in front of the positioning plate and the height of the clamping plate is smaller than that of the positioning plate; a horizontally-arranged pressing rod is arranged on the positioning plate; the extension direction of the pressing rod is towards the clamping plate; the pressing rod is arranged above the clamping plate and is arranged corresponding to the clamping plate; a plurality of column bodies which are arranged in the circumferential direction are arranged on the positioning plate in a way of encircling the pressing rod; and the column bodies are arranged in an outer protruding way. According to the inner hole machining device disclosed by the invention, the inner hole of a workpiece is positioned by the column bodies, and the inner wall of the inner hole is in contact with the peripheries of the column bodies, so that the contact area of the inner hole and a clamping tool is reduced, the clamping difficulty of the inner hole on a fixture is reduced, and the damage to the workpiece is avoided.