To provide an optimal intake air efficiency by simplifying and miniaturizing a structure, and reducing the weight of an intake manifold having a variable intake mechanism and varying the capacity of a collector according to the operation state of an engine in the engine for an automobile which as a wide use rotation speed range and is difficult to hold a state of the favorable intake air efficiency in the whole range.

An intake channel of the intake manifold 1 is constituted of the collector 4, independent intake pipes 5a, 5b, and 5c, sub-collectors 7a and 7b partially jointly installed with the independent intake pipes 5a, 5b, and 5c and disposed on the upper part of an engine flange 6, and a plurality of communication valves controlling the communication. The communication valves are characterized in being opened/closed or continuously controlled based on the engine rotation speed and varying the collector capacity.