To judge abnormality of a pressure measurement system measuring a pressure change quantity in an evaporated fuel treatment device for an internal combustion engine controlling flow rate of air fuel mixture introduced from a canister to an intake pipe, based on pressure change quantity of air and air fuel mixture by a restrictor.

A pump is driven and air is circulated to the restrictor (S22) when power is supplied to a device for a first time. Then, pressure drop quantity (pressure difference ΔP1) due to the restrictor is detected (S23) and is stored in EEPROM as an initial value ΔP1(0). Then, pressure difference ΔP1 measured when air is circulated to the restrictor is compared with the initial value ΔP1(0) for flow rate control. Since pressure difference ΔP1 is not so different from the initial value ΔP1(0) if there is no abnormality in the pressure measurement system, abnormality of the pressure measurement system is judged by comparing both.

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