A cam phase control system for an internal combustion engine, which is capable of suppressing deviation of the cam phase which is caused by a sudden change in the engine speed due to the structure of a variable cam phase mechanism, thereby securing excellent controllability and high control accuracy. The coma phase control system of the engine comprise an ECU and an electromagnetic variable cam phase mechanism. The ECU calculates an SLD control input for causing the cam phase to converge to a target cam phase by equations (1) to (6), calculates a gain-adjusted value by modulating the SLD control input by equations (20) to (25), calculates a correction value according to the engine speed NE, and calculates a control input for controlling the variable cam phase mechanism by correcting the gain-adjusted value by the correction value.