To accurately measure intake air amount and to protect an air flow sensor in an intake air amount measuring instrument for an internal combustion engine.

An intake air amount measuring portion (24) includes a first intake branched path (26) and a second intake branched path (27) configuring a part of an intake path (14). The first intake branched path (26) has an air flow sensor (29) and a first control valve (30) for controlling the intake air amount to the first intake branched path (26) on the downstream side of the air flow sensor (29) disposed. The second intake branched path (27) has a second control valve (31) for controlling the intake air amount to the second intake branched path (27) disposed.