PURPOSE: To reduce the output error by fitting an air flow meter so that the moving direction of a movable body is made within the preset angle with respect to the longitudinal direction of a vehicle in the air flow meter provided with the movable body moved in an intake passage in response to the suction air quantity.

CONSTITUTION: An air flow meter 11 is located in a tube body 100 located at the most upstream side of an outer tube 10 constituted of three tube bodies 100W300, and a movable body 30 is stored in it movably in the axial direction. The outer cylinder 32 of the movable body 30 is slidably coupled with the large-diameter tube 230 of the tube body 200, a shaft 40 connected to the movable body 30 is supported by the smell-diameter tube 250 of the tube body 200 via bearings 41, 42, thus the movable body 30 is moved and guided. The signal utilized to calculate the suction air quantity as this movable body 30 is moved is outputted from a potentiometer 50. In this case, the air flow meter 11 is arranged so that the moving direction of the movable body 30 is made within 30° with respect to the longitudinal direction of a vehicle.