To introduce a large quantity of exhaust gas recirculation (EGR) gas into a combustion chamber of an engine to achieve both reduction in NOx and improvement in fuel efficiency.

A phase and amplitude conversion mechanism disposed in an EGR introduction flow path of an EGR system is configured to perform two types of EGR valve opening control, a first EGR valve opening control and a second EGR valve opening control, such that the opening timing of an intake valve of the engine matches the timing of the peak in the pressure pulsation of exhaust gas, and the amplitudes of the pressure pulsation of exhaust gas before a first EGR valve and a second EGR valve are smaller than the amplitude of the pressure pulsation of the exhaust gas before a dividing section. As a result, exhaust gas pulsation having arbitrary phase and amplitude can be generated. In addition, at the timing at which the intake valve is open, pressure difference between an intake path and the EGR introduction flow path can be increased. Therefore, a large quantity of EGR gas can be introduced into the combustion chamber of the engine.