In a flow meter with a displacement meter (1) a parallel-connected pressure difference sensor (3) has a bypass channel (8) which frees a connection between the inflow side and the outflow side (4, 5) when a piston (7) butts against a maximum stroke stop (9). In the bypass channel (8) is a check valve (11) which prevents the backflow from the outflow side to the inflow side (5, 4) and thus enables a return of the piston (7) purely due to pressure.