PURPOSE: To provide an internal-combustion engine with enhanced characteristics of the intake gas filling efficiency while the iontake dia. of the engine is compacted.

CONSTITUTION: In the low speed operating range of an engine a first valve 8 to open and shut a capacity chamber 31 partitioned in an air cleaner 3 is closed while a second valve 9 mounted at the downstream end of a second intake pipe 6 is opened, to release only a first intake pipe 5, and an intake gas collector part 4 is put in communication with the capacity chamber 31 throgh the second intake pipe 6 so as to generate a high intake gas filling efficiency having a peak on the low speed side. In the medium and super-high speed ranges, the first and second valves 8, 9 are opened to attain a high intake gas filling efficiency having peaks in respective ranges. In the high speed range, the first valve 8 is opened and the second 9 shut to obtain a high intake gas filling efficiency having a peak in the high speed range. Thereby a characteristic of intake gas filling efficiency is established, which gives high efficiency in all ranges and presents a small change from range to range.