A steer-by-wire steering system, comprising: a steering device including a steering motor and configured to steer one or more wheels mechanically independently of an operation force of an operating member; and a controller configured to supply a steering current to the steering motor based on a steering request to control the steering motor, wherein the controller includes: a plurality of calculating portions (51, 54, 57) communicably connected to each other, each of the plurality of calculating portions (51, 54, 57) being configured to calculate a current value of the steering current based on the steering request; a plurality of drive circuits (52, 55, 58) respectively corresponding to the plurality of calculating portions (51, 54, 57), each of the plurality of drive circuits (52, 55, 58) being configured to supply the steering current to the steering motor based on control of a corresponding one of the plurality of calculating portions (51, 54, 57); and a plurality of temperature sensors (52, 55, 58) respectively corresponding to the plurality of calculating portions (51, 54, 57), each of the plurality of temperature sensors (53, 56, 59) being configured to detect a temperature of a corresponding one of the plurality of calculating portions (51, 54, 57), wherein, when a detection temperature difference that is a difference between detection temperatures of any two of the plurality of temperature sensors (53, 56, 59) is greater than a predetermined threshold, each of the plurality of calculating portions (51, 54, 57) executes an independent calculation control to independently calculate and set a current limit value, which is an upper limit value of the steering current, based on a detection temperature of one of the plurality of temperature sensors (53, 56, 59) corresponding to itself, irrespective of detection temperatures of one or more of the plurality of temperature sensors (53, 56, 59) other than the one of the plurality of temperature sensors (53, 56, 59) corresponding to itself. a steering device including a steering motor and configured to steer one or more wheels mechanically independently of an operation force of an operating member; and a controller configured to supply a steering current to the steering motor based on a steering request to control the steering motor, wherein the controller includes: a plurality of calculating portions (51, 54, 57) communicably connected to each other, each of the plurality of calculating portions (51, 54, 57) being configured to calculate a current value of the steering current based on the steering request; a plurality of drive circuits (52, 55, 58) respectively corresponding to the plurality of calculating portions (51, 54, 57), each of the plurality of drive circuits (52, 55, 58) being configured to supply the steering current to the steering motor based on control of a corresponding one of the plurality of calculating portions (51, 54, 57); and a plurality of temperature sensors (52, 55, 58) respectively corresponding to the plurality of calculating portions (51, 54, 57), each of the plurality of temperature sensors (53, 56, 59) being configured to detect a temperature of a corresponding one of the plurality of calculating portions (51, 54, 57), a plurality of calculating portions (51, 54, 57) communicably connected to each other, each of the plurality of calculating portions (51, 54, 57) being configured to calculate a current value of the steering current based on the steering request; a plurality of drive circuits (52, 55, 58) respectively corresponding to the plurality of calculating portions (51, 54, 57), each of the plurality of drive circuits (52, 55, 58) being configured to supply the steering current to the steering motor based on control of a corresponding one of the plurality of calculating portions (51, 54, 57); and a plurality of temperature sensors (52, 55, 58) respectively corresponding to the plurality of calculating portions (51, 54, 57), each of the plurality of temperature sensors (53, 56, 59) being configured to detect a temperature of a corresponding one of the plurality of calculating portions (51, 54, 57), wherein, when a detection temperature difference that is a difference between detection temperatures of any two of the plurality of temperature sensors (53, 56, 59) is greater than a predetermined threshold, each of the plurality of calculating portions (51, 54, 57) executes an independent calculation control to independently calculate and set a current limit value, which is an upper limit value of the steering current, based on a detection temperature of one of the plurality of temperature sensors (53, 56, 59) corresponding to itself, irrespective of detection temperatures of one or more of the plurality of temperature sensors (53, 56, 59) other than the one of the plurality of temperature sensors (53, 56, 59) corresponding to itself.