An intake system of an internal combustion engine, in which a phase angle between throttle valves is provided in order to perform combustion appropriate for each cylinder so as to stabilize a number of revolutions and thereby suppress generation of unburned gas, is provided. The intake system is provided to intake passages of an internal combustion engine with parallel cylinders. The intake system includes a power transmission mechanism configured to transmit power from a power source to throttle shafts so as to synchronize and simultaneously turn a plurality of throttle valves and thereby open and close the intake passages. At least one of the throttle valves is an angled throttle valve having a phase angle at an open position relative to the other throttle valve.