PURPOSE: To obtain a response time tester for determining that the response time of an air mass flow sensor comes within a specified limit.

CONSTITUTION: The response time tester comprises a connector 28 coupled with a sensor manifold 12 fixed with an air mass flow sensor 10, and a main manifold 30 coupled between a vacuum source 46 and the connector. The main manifold comprises first and second branches 32, 38 in parallel wherein the former is provided with a first sonic nozzle 34 and a first valve 36 while the latter is provided a second sonic nozzle 40 and a second valve 42. An electric controller 50 energizes the valve continuously to change the air flow stepwise and the output signal therefrom is recorded and then the response time thereof is compared with a reference value. This arrangement realizes a tester for detecting an air mass flow sensor having a response time longer than a specified value.