An intake manifold includes a manifold case having an intake passage. A valve is arranged in the intake passage. The valve is rotatable about its proximal end so as to partly close the intake passage. When the valve partly closes the intake passage, a clearance is formed between a wall surface defining the intake passage and a distal end of the valve. The clearance connects a section of the intake passage upstream of the valve and a section of the intake passage downstream of the valve to each other. When the valve partly closes the intake passage, each of side edges of the valve comes in surface-to-surface contact with a portion of the intake passage wall surface that faces the side edge of the valve, thereby airtightly sealing the spaces between the side edges of the valve and the wall surface of the intake passage.