Hydraulic shifting actuator of a gearbox, in particular a mechanically unsynchronized gearbox, which has shifting positions for a first shift stage of the gearbox, for a second shift stage of the gearbox and for a neutral position of the gearbox, which neutral position forms an idling position, wherein the shifting actuator has a shift piston which can be displaced longitudinally in a housing bore of a housing and is provided with a piston rod and a piston section which is arranged on the piston rod, wherein a first control pressure face is configured on a first end side of the piston section, which first control pressure face is connected to a first control pressure space, wherein, in the case of a control pressure which prevails in the first control pressure space, the shift piston can be actuated into the shifting position for the first shift stage, and a second control pressure face is configured on a second end side of the piston section which lies opposite the first end side, which second control pressure face is connected to a second control pressure space, wherein, in the case of a control pressure which prevails in the second control pressure space, the shift piston can be actuated into the shifting position for the second shift stage, wherein two step pistons (10a, 10b) are provided which are arranged such that they can be displaced longitudinally coaxially with respect to the piston rod of the shift piston, and through which step pistons (10a, 10b) the piston rod of the shift piston is guided, wherein the first step piston is arranged such that it can be displaced longitudinally in the first control pressure space and has a control face which is loaded by the control pressure which prevails in the first control pressure space, wherein the first step piston can be brought into an operative connection by way of an inner end side with the first end side of the piston section of the shift piston, wherein the second step piston is arranged such that it can be displaced longitudinally in the second control pressure space and has a control face which is loaded by the control pressure which prevails in the second control pressure space, wherein the second step piston can be brought into an operative connection by way of an inner end side with the second end side of the piston section of the shift piston, wherein an annular gap is configured between an internal diameter of the first step piston and the external diameter of the piston rod, via which annular gap the first end side of the piston section of the shift piston is connected to the first control pressure space, and wherein an annular gap is configured between an internal diameter of the second step piston and the external diameter of the piston rod, via which annular gap the second end side of the piston section of the shift piston is connected to the second control pressure space, wherein a first stop for the first step piston which limits the maximum stroke of the shift piston in the second shift stage and a second stop for the second step piston which limits the maximum stroke of the shift piston in the first shift stage are configured on the housing, wherein the housing bore is configured on both sides of the piston section as a stepped bore, in which in each case one step piston (10a; 10b) is arranged such that it can be displaced longitudinally, wherein the piston section of the shift piston is arranged in a central section of reduced diameter of the stepped bore, the first step piston is arranged with an inner section of reduced diameter, on which the inner end side is configured, in the central section of the stepped bore and with an outer section of increased diameter in an outer section of increased diameter of the stepped bore, which outer section forms the first control pressure space, and the second step piston is arranged with an inner section of reduced diameter, on which the inner end side is configured, in the central section of the stepped bore and with an outer section of increased diameter in an outer section of increased diameter of the stepped bore, which outer section forms the second control pressure space, characterized in that the gearbox is a mechanical two-gear gearbox, and the respective step piston (10a, 10b) is sealed with respect to the central section of the stepped bore and with respect to the outer section of the stepped bore.