To execute intake air quantity control by a variable valve mechanism while ensuring a necessary requested negative pressure, in a control system for an internal combustion engine requiring a suction negative pressure.

If a brake master vac, a fuel vapor purge control system and a blowby gas control system request a negative pressure while a throttleless operation is requested for intake air quantity control by the variable valve mechanism capable of varying an operating angle, a valve lift and the like under a fixed throttle valve opening, a target negative pressure is computed according to the request level, a target throttle valve opening is computed so as to produce the target negative pressure, and throttle valve opening is regulated accordingly.