PURPOSE: To provide an intake air control device of a gasoline engine capable of maintaining its startability at low temperature.

CONSTITUTION: A diaphragm 4 which moves upward relative to a lower inner wall 1c of an intake air manifold 1 is installed on the lower inner wall 1c of the intake air manifold 1 at its upwardly bent part. Also an air pipe 6 is installed connectedly through a hole 5 between the lower inner wall 1c of the intake air manifold 1 and the diaphragm 4. To the air pipe 6, a pipe 6a to which exhaust gas is led through a solenoid valve 8 and a pipe 6b connected to fresh air are connected. Then a water temperature sensor 10 for detecting water temperature of cooling water is installed in a cooling water jacket W. When the water temperature of the cooling water detected by the water temperature sensor 10 at start of an engine is lower than a reference value, a control unit 9 drives the solenoid valve 8 to connect a first pipe to the air pipe 6 and move the diaphragm 4 upward.