A pneumatically driven setting tool for driving in fastening elements, includes a chamber (17) forming a storage chamber (22) for storing the pressure medium produced by the compression device (30, 130) and an expansion chamber (26) adjoining the drive-in piston (13), which is displaceable in a guide (12), at a side of the drive-in piston (13) remote from the piston stem (14), communicating with the storage chamber (22), and having an opening (18) connecting the expansion chamber (26) with the drive-in piston (13), at least one check valve (44, 54, 142) arranged between the compression device (30, 130) and the chamber (17), and a piston retaining device (47) for retaining the drive-in piston (13) in its initial position (80) in which the chamber (17) is sealed against the guide (12).