Intake apparatus of internal combustion engine

An intake apparatus of an internal combustion engine for supplying an air to a combustion chamber of the internal combustion engine, comprising:

• a variable intake passage having a passage length from an air introducing portion to said combustion chamber configured to be changeable, the variable intake passage being made of a tubular space that is formed with a fixed member and a movable member arranged to face the fixed member and having a relative position with said fixed member changed, the movable member being moved to make a position of said air introducing portion farther from or closer to said combustion chamber to increase or decrease the passage length, wherein
• said variable intake passage has a cross section that gradually increases from an upstream side to a downstream side in an air introducing direction,
• wherein said fixed member is an outer tube and said movable member is an inner tube that is supported by the outer tube constituting said fixed member in a coaxial and relatively rotatable manner, and wherein the inner tube constituting said movable member is rotated in a normal or opposite direction about its central axis to continuously change the passage length of said variable intake passage, and
• wherein the outer tube constituting said fixed member has an inner peripheral groove, and the inner tube constituting said movable member has an outer peripheral groove that faces the inner peripheral groove of said fixed member to form a tubular space, and wherein at least one of the inner peripheral groove of said fixed member and the outer peripheral groove of said movable member has a groove depth that gradually increases from the upstream side to the downstream side in the air introducing direction of said variable intake passage.