A device for administering a fluid, comprising a cylinder, which has an open dispensing end, a piston, which is displaceable in the cylinder between a front end position and a rear end position and is connected to a piston rod which, along a first direction, protrudes from a rear end of the cylinder opposite the open dispensing end, a nonreturn valve closing the open dispensing end, and a tensioning device connected to the piston rod; wherein the tensioning device can move the piston rod along the first direction in a tensioning procedure until the piston is in its rear end position, in order thereby to fill the cylinder with the fluid to be administered and to pretension the piston rod toward the open dispensing end, and wherein the tensioning device, when the piston is in its rear end position, can release the piston rod in a dispensing procedure such that, owing to the pretension which is present, the piston is moved counter to the first direction toward the open dispensing end and, in the process, fluid in the cylinder is dispensed via the nonreturn valve for administration, characterized in that the tensioning device has a ramp which is rotatable by means of a motor and has a ramp track extending along a helical line, wherein the ramp track ascends from a first plateau along a region of inclination to a second plateau and descends from the second plateau to the first plateau via a transition flank, wherein the ramp track has a transfer region connecting the second plateau and the transition flank, wherein the tensioning device moreover has a roller which is in contact with the ramp track and which is mounted rotatably in a driver, the latter being connected to the piston rod, and therefore, upon rotation of the ramp along a first rotation direction, the ramp track runs below the thus rotating roller, wherein, for the tensioning procedure, the ramp track is rotated along the first rotation direction such that the roller runs on the region of inclination as far as the second plateau and the piston is thereby moved to its rear end position, wherein, for the dispensing procedure, starting from a contact of the roller with the second plateau, the ramp track is rotated along the first rotation direction until the roller runs over the transfer region and, on account of the tensioning, is accelerated toward the first plateau and, as a result, the piston is moved toward the open dispensing end, wherein the piston rod is connected to the driver via a joint. a cylinder, which has an open dispensing end, a piston, which is displaceable in the cylinder between a front end position and a rear end position and is connected to a piston rod which, along a first direction, protrudes from a rear end of the cylinder opposite the open dispensing end, a nonreturn valve closing the open dispensing end, and a tensioning device connected to the piston rod; wherein the tensioning device can move the piston rod along the first direction in a tensioning procedure until the piston is in its rear end position, in order thereby to fill the cylinder with the fluid to be administered and to pretension the piston rod toward the open dispensing end, and wherein the tensioning device, when the piston is in its rear end position, can release the piston rod in a dispensing procedure such that, owing to the pretension which is present, the piston is moved counter to the first direction toward the open dispensing end and, in the process, fluid in the cylinder is dispensed via the nonreturn valve for administration, characterized in that the tensioning device has a ramp which is rotatable by means of a motor and has a ramp track extending along a helical line, wherein the ramp track ascends from a first plateau along a region of inclination to a second plateau and descends from the second plateau to the first plateau via a transition flank, wherein the ramp track has a transfer region connecting the second plateau and the transition flank, wherein the tensioning device moreover has a roller which is in contact with the ramp track and which is mounted rotatably in a driver, the latter being connected to the piston rod, and therefore, upon rotation of the ramp along a first rotation direction, the ramp track runs below the thus rotating roller, wherein, for the tensioning procedure, the ramp track is rotated along the first rotation direction such that the roller runs on the region of inclination as far as the second plateau and the piston is thereby moved to its rear end position, wherein, for the dispensing procedure, starting from a contact of the roller with the second plateau, the ramp track is rotated along the first rotation direction until the roller runs over the transfer region and, on account of the tensioning, is accelerated toward the first plateau and, as a result, the piston is moved toward the open dispensing end, wherein the piston rod is connected to the driver via a joint.