To provide a compact air blow device capable of surely removing water adhering to a lid member at a low cost.

A support jig 2 includes a storage recess 22 which is opened upward to store a shaft section 10a of an oil supply cap 10 from the above and supports a head 10b of the oil supply cap 10 at an open port peripheral edge of the storage recess 22 in a state in which the shaft section 10a is stored in the storage recess 22. Air discharge means 3 includes two discharge ports 33a facing the storage recess 22 and discharges air W in an anti-tightening direction X in a tangential direction of the shaft section 10a toward a male screw section 10c of the shaft section 10a stored in the storage recess 22.