PURPOSE: To make possible the maintaining of a measuring accuracy sufficiently even against heat as well by providing a second metal member to reduce the deflection of a metal screen as first metal member of a rectifier grating as caused by thermal shrinkage of a resin frame part at the rectifier grating.

CONSTITUTION: A body 2 comprising a resin is constituted of an air path 6, a sensor 4 for detecting an air flow rate and a rectifier grating 3 set on the upper side of the sensor for the flow of air 5. A frame part 8 of the rectifier grating 3 is made of a resin between a metal screen 7 as the first metal member and a second metal member 9. As a result, when the body 2 and the frame part 8 of the rectifier grating 3 comprising the resin as expanded by heat generated in an internal combustion engine are shrunk thermally, the second metal member 9 provided on the rectifier grating 3 prevents a force working on the metal screen 7 as the first metal member of the rectifier grating 3 as generated by the thermal shrinkage thereby making possible the reduction of measuring errors owing to the deformation of the metal screen 7.