An intake air control device movable in response to an acceleration pedal for an internal combustion engine comprising: a throttle body having an intake conduit to the internal combustion engine; a throttle valve having a shaft rotatably held in the throttle body for opening and closing the intake conduit; a rotary member made of non-magnetic metal and rigidly fixed to the shaft for driving the shaft in response to the acceleration pedal so as to rotate the throttle valve; and a non-contact type angular position detector having a magnetic flux generating member (41, 42) and a magnetic flux detecting element, the magnetic flux generating member being attached to the rotary member so as to rotate together therewith and the magnetic flux detecting element being stationarily positioned to face the magnetic flux generating member with an air gap therebetween, wherein the magnetic flux detecting element generates an electric signal in response to a change of magnetic flux applied thereto from the magnetic flux generating member so that an angular position of the shaft driven by the rotary member is detected, characterised in that, the rotary member is formed in a cup-shape whose bottom wall is fixed to an end face of the shaft and whose inner circumferential wall is provided with the magnetic flux generating member, and wherein the magnetic flux detecting element is accommodated in an inside space formed by the cup-shaped rotary member, the magnetic flux generating member (41, 42) comprises a pair of permanent magnets provided at an inner peripheral surface of the cup-shaped rotary member; and a pair of yokes provided between the pair of the permanent magnets and at the inner peripheral surface of the cup-shaped rotary member. a throttle body having an intake conduit to the internal combustion engine; a throttle valve having a shaft rotatably held in the throttle body for opening and closing the intake conduit; a rotary member made of non-magnetic metal and rigidly fixed to the shaft for driving the shaft in response to the acceleration pedal so as to rotate the throttle valve; and a non-contact type angular position detector having a magnetic flux generating member (41, 42) and a magnetic flux detecting element, the magnetic flux generating member being attached to the rotary member so as to rotate together therewith and the magnetic flux detecting element being stationarily positioned to face the magnetic flux generating member with an air gap therebetween, wherein the magnetic flux detecting element generates an electric signal in response to a change of magnetic flux applied thereto from the magnetic flux generating member so that an angular position of the shaft driven by the rotary member is detected, characterised in that, the rotary member is formed in a cup-shape whose bottom wall is fixed to an end face of the shaft and whose inner circumferential wall is provided with the magnetic flux generating member, and wherein the magnetic flux detecting element is accommodated in an inside space formed by the cup-shaped rotary member, the magnetic flux generating member (41, 42) comprises a pair of permanent magnets provided at an inner peripheral surface of the cup-shaped rotary member; and a pair of yokes provided between the pair of the permanent magnets and at the inner peripheral surface of the cup-shaped rotary member.