A method is for adjusting a flow measuring device that includes a housing and a flow sensor. The housing includes a bypass flow passage which is formed to take in a part of a mainstream of air. The sensor is disposed in the bypass flow passage and outputs an electrical signal in accordance with a flow rate of air. The bypass flow passage is formed in an asymmetrical shape with respect to the sensor in upstream and downstream directions of the mainstream. A flow from an upstream side toward a downstream side of the mainstream is a forward flow. A flow from the downstream side toward the upstream side of the mainstream is a backward flow. According to the method, an output from the sensor in a backward-flow region is obtained. Furthermore, the output of the sensor in the backward-flow region is adjusted to have a desired output characteristic.