To improve an inner surface honing performance by ensuring the proper injection of a grinding fluid to the grinding part of the inner surface of a cylinder as a workpiece.

A main shaft 8 with a honing head mounted on the end is held on a head stock 6, so as to be rotated on the operation of a motor 9, and a hollow advance and retreat rod 17 is laid within the center of the main shaft 8, so as to cause the advance and retreat of a grinding wheel mounted on the periphery of the honing head. Furthermore, a fluid pressure cylinder 40 is fastened to the head stock 6 for moving in and out the hollow advance and retreat rod 17, so as to keep a piston rod 41 aligned with the rear end thereof, and the piston rod 41 is formed to be hollow type communicated to the rod 17. Also, the rear end of the piston rod 41 is projected from the fluid pressure cylinder 40, and a lubrication plug 43 is connected to the projected end of the piston rod 41. A grinding fluid is thereby fed to the honing head forcibly via the rod 17 and injected from a nozzle hole.