There is provided an ignition timing control device for an internal combustion engine capable of appropriately performing knock learning by performing knock learning adapted to an engine combustion phenomenon. The inventor has found the principle of a knock reduction effect due to ignition retard is that “if a combustion period moves toward the retard side, a cylinder volume during the combustion period increases, resulting in curbing of rise in the temperature and pressure of unburned gas”. An ignition timing control device according to the present invention is capable of new knock learning based on the principle, which learns a “cylinder volume rate”. The cylinder volume rate is a parameter determined from the amount of change in cylinder volume. Even when an operational status changes, learned ignition timing obtained from knock control means can be set to an appropriate value by reflecting the learned cylinder volume rate.