A thermal air flow meter consists essentially of a hollow cylindrical support made of an insulating material, a heat-sensitive resistor formed on top of the support, and lead wires inserted into the hollow part of the support from either end and bonded thereto by glass. This flow meter measures the flow rate from changes in the resistance of the heat-sensitive resistor with temperature. The ratio of the inner diameter d.sub.2 of the support to the outer diameter d.sub.3 of the lead wires (d.sub.2 /d.sub.3) is at least 1.7. This arrangement can provide a thermal air flow meter with a quick response to changes in flow rate.