An operation circuit for a work vehicle drives an electromagnetic actuator by generating an operation signal corresponding to a switch operation and drives a work actuator in response to the drive of the electromagnetic actuator. By installing a specific detachable electric circuit unit in a first operation circuit that generates a first operation signal in response to an operation of a specific switch, the first operation circuit can be modified to a second operation circuit that generates a second operation signal different from the first operation signal in response to an operation of the same switch.