A device for detecting a rail load; which device can be fitted into a bore of a rail; on which rail travel rail vehicles with wheels, said wheels exerting a load onto the rail; wherein said device comprises a sensor, which sensor generates a load signal (S, S') under the action of the rail load, said load signal (S, S') being a measure for the rail load; wherein said device comprises a sensor housing in the shape of a circular cylinder; which sensor housing comprises a cavity, and wherein the sensor is arranged within the cavity; wherein the sensor housing is delimited by a lateral surface; said lateral surface having an oversize with respect to a bore radius of the bore in at least one peripheral surface area (37°) that has a larger dimension; wherein the device having said oversize can be fitted into the bore of the rail by two form- and force-fit connections (33, 33`) in the peripheral surface area (37°) having said larger dimension of the lateral surface, characterized in that the sensor comprises at least one piezoelectric sensor element (321, 321'), which piezoelectric sensor element (321, 321') generates electric polarization charges serving as the load signal (S, S'); in that within the cavity two punches (36, 36') extend along a longitudinal axis towards a center of the sensor housing; in that the two punches (36, 36') are made integrally with the sensor housing; and in that the two punches (36, 36') hold the sensor; in that a small fraction of the rail load acts via a rail body along a vertical axis onto the two form- and force-fit connections (33, 33') in the peripheral surface area (37°) having the larger dimension of the lateral surface onto the sensor housing; and in that an even smaller fraction of the rail load acts from the sensor housing along the longitudinal axis via the two punches (36, 36') onto the sensor that comprises the piezoelectric sensor element (321, 321'). wherein said device comprises a sensor housing in the shape of a circular cylinder; which sensor housing comprises a cavity, and wherein the sensor is arranged within the cavity; wherein the sensor housing is delimited by a lateral surface; said lateral surface having an oversize with respect to a bore radius of the bore in at least one peripheral surface area (37°) that has a larger dimension; wherein the device having said oversize can be fitted into the bore of the rail by two form- and force-fit connections (33, 33`) in the peripheral surface area (37°) having said larger dimension of the lateral surface, characterized in that the sensor comprises at least one piezoelectric sensor element (321, 321'), which piezoelectric sensor element (321, 321') generates electric polarization charges serving as the load signal (S, S'); in that within the cavity two punches (36, 36') extend along a longitudinal axis towards a center of the sensor housing; in that the two punches (36, 36') are made integrally with the sensor housing; and in that the two punches (36, 36') hold the sensor; in that a small fraction of the rail load acts via a rail body along a vertical axis onto the two form- and force-fit connections (33, 33') in the peripheral surface area (37°) having the larger dimension of the lateral surface onto the sensor housing; and in that an even smaller fraction of the rail load acts from the sensor housing along the longitudinal axis via the two punches (36, 36') onto the sensor that comprises the piezoelectric sensor element (321, 321').