The invention relates to a pulsation controller in the intake/exhaust systems of internal combustion engines inclusive of two-cycle gasoline engines, four-cycle engines and rotary piston engines, and includes a device for detecting by means of a sensor pulsation in the intake/exhaust pipes connected to a cylinder, and a control means for allowing the desired pressure wave in the pulsation to coincide with the given position of the intake/exhaust system by the detection result obtained by this sensor. The phase of a standing wave in the intake/exhaust system of the engine is detected to control the impedance or the timing for opening and closing valves or ports in the intake/exhaust system and, hence, the phase of a standing wave in the intake/exhaust system, thereby improving the intake/exhaust efficiency for more efficient operation.