An intake apparatus for an internal combustion engine equipped with an air cleaner, comprising: two intake ducts (6, 7) connected to an intake inlet of the air cleaner; and a flap mechanism disposed in one of the two intake ducts (6, 7), the flap mechanism serving for opening and closing the one of the two intake ducts in response to intake air flow entering into the one of the two intake ducts (6, 7), the flap mechanism comprising: a plate-shaped main flap supported at one end portion thereof so as to be rotatable about a rotation axis between a fully opening position and a fully closing position, the rotation axis being located at the one end portion of the main flap, a plate-shaped damper flap disposed to make a predetermined angle between the main flap and the damper flap with respect to the rotation axis, the damper flap making a unitary rotation with the main flap, a damper chamber formed in a portion of an outer wall of the one of the two intake ducts (6, 7) so as to be recessed along a trace of rotational movement of the damper flap, the damper chamber cooperating with the damper flap to form a damper space therebetween, and a biasing member that biases the main flap in a closing direction; wherein when the main flap is located in an angular range between the fully closing position and a predetermined opening angle, a peripheral edge of the damper flap is opposed to an inner wall surface of the damper chamber with a fine clearance so that the damper space is rendered substantially closed, and when the main flap is located with an opening angle larger than the predetermined opening angle, a communication passage that serves to open the damper space is formed between the inner wall surface of the damper chamber and the peripheral edge of the damper flap. two intake ducts (6, 7) connected to an intake inlet of the air cleaner; and a flap mechanism disposed in one of the two intake ducts (6, 7), the flap mechanism serving for opening and closing the one of the two intake ducts in response to intake air flow entering into the one of the two intake ducts (6, 7), the flap mechanism comprising: a plate-shaped main flap supported at one end portion thereof so as to be rotatable about a rotation axis between a fully opening position and a fully closing position, the rotation axis being located at the one end portion of the main flap, a plate-shaped damper flap disposed to make a predetermined angle between the main flap and the damper flap with respect to the rotation axis, the damper flap making a unitary rotation with the main flap, a damper chamber formed in a portion of an outer wall of the one of the two intake ducts (6, 7) so as to be recessed along a trace of rotational movement of the damper flap, the damper chamber cooperating with the damper flap to form a damper space therebetween, and a biasing member that biases the main flap in a closing direction; wherein when the main flap is located in an angular range between the fully closing position and a predetermined opening angle, a peripheral edge of the damper flap is opposed to an inner wall surface of the damper chamber with a fine clearance so that the damper space is rendered substantially closed, and when the main flap is located with an opening angle larger than the predetermined opening angle, a communication passage that serves to open the damper space is formed between the inner wall surface of the damper chamber and the peripheral edge of the damper flap. a plate-shaped main flap supported at one end portion thereof so as to be rotatable about a rotation axis between a fully opening position and a fully closing position, the rotation axis being located at the one end portion of the main flap, a plate-shaped damper flap disposed to make a predetermined angle between the main flap and the damper flap with respect to the rotation axis, the damper flap making a unitary rotation with the main flap, a damper chamber formed in a portion of an outer wall of the one of the two intake ducts (6, 7) so as to be recessed along a trace of rotational movement of the damper flap, the damper chamber cooperating with the damper flap to form a damper space therebetween, and a biasing member that biases the main flap in a closing direction; wherein when the main flap is located in an angular range between the fully closing position and a predetermined opening angle, a peripheral edge of the damper flap is opposed to an inner wall surface of the damper chamber with a fine clearance so that the damper space is rendered substantially closed, and when the main flap is located with an opening angle larger than the predetermined opening angle, a communication passage that serves to open the damper space is formed between the inner wall surface of the damper chamber and the peripheral edge of the damper flap.