Magnetic rotation sensor

A rotation-angle-detection device (28) includes a main housing (15), a resinous cover (24) for covering an opening of the main housing (15), a permanent magnet (22) disposed at the main housing (15) to be rotatable in response to rotation of a throttle valve (11), and a magnetic sensor (25). The cover (24) is longer in longitudinal direction than in lateral direction, and the magnetic sensor (25) is fixed to the resinous cover (24). The magnetic sensor (25) is disposed so that the detection direction and the longitudinal direction of the cover (24) cross each other at a right angle.