A new internal grinding machine has been designed to obtain very high accuracy in automatic sizing grinding. Hydraulic systems employed in ordinary grinder as power transmission and control system are completely removed, The wheel head oscillating mechanism is driven by constant speed cam ane link for traversing grinding, the wheel head is infed by cam and the internal grinding spindle is driven by high frequency motor. This internal grinder realized the sufficiently small piece-to-piece fluctuation and the very slow deviation from set value in dimentional sccuracy of work piece.