The present invention provides an intake air control capable of implementing a highly accurate constant negative pressure control with a smaller number of process steps under various environments. The intake air control is applicable to an engine having a variable valve actuation mechanism for adjusting at least a lift amount of an intake valve to control an intake air amount and a throttle valve for keeping a gauge pressure in an intake manifold at a desired gauge pressure. A reference throttle opening area is determined by referring to a first table based on a desired intake air amount. The first table defines a relation between an intake air amount and a throttle opening area under a reference gauge pressure, a reference atmospheric pressure and a reference intake air temperature. A throttle opening area for achieving the desired gauge pressure is determined by correcting the reference throttle opening area with a correction parameter derived based on the Bernoulli's law by using the desired gauge pressure, a current atmospheric pressure and a current intake air temperature.