A traveling transmission device of a tractor comprising: a speed changer device for speed-changing power from an engine and output it, the speed changer device including a stepless speed changer section to which a power of the engine is inputted, a composite planetary transmission section to which an output of the stepless speed changer section and the power of the engine are inputted, and a stage-divided transmission section configured to output the output of the composite planetary transmission section in divided stages; a forward/reverse switchover device configured to switch the output of the speed changer device into/between a forward traveling power and a reverse traveling power; a rear wheel differential mechanism provided rearwardly of the speed changer device and configured to input the output of the forward/reverse switchover device and transmit it to rear wheels; a gear transmission mechanism configured to transmit power of an output shaft of the forward/reverse switchover device to an input shaft of the rear wheel differential mechanism; and a transmission case accommodating the speed changer device, the forward/reverse switchover device, the rear wheel differential mechanism and the gear transmission mechanism; wherein the transmission case includes a front case portion which accommodates the speed changer device and a rear case portion which accommodates the forward/reverse switchover device, the rear wheel differential mechanism and the gear transmission mechanism, with the front case portion and the rear case portion being separable from each other; characterized in that: the gear transmission mechanism is detachably attached to a portion of inside of the transmission case which portion corresponds to a front end portion of the rear case portion; and the rear case portion is separable into the front end portion of the rear case portion and another portion of the rear case portion than the front end portion. a speed changer device for speed-changing power from an engine and output it, the speed changer device including a stepless speed changer section to which a power of the engine is inputted, a composite planetary transmission section to which an output of the stepless speed changer section and the power of the engine are inputted, and a stage-divided transmission section configured to output the output of the composite planetary transmission section in divided stages; a forward/reverse switchover device configured to switch the output of the speed changer device into/between a forward traveling power and a reverse traveling power; a rear wheel differential mechanism provided rearwardly of the speed changer device and configured to input the output of the forward/reverse switchover device and transmit it to rear wheels; a gear transmission mechanism configured to transmit power of an output shaft of the forward/reverse switchover device to an input shaft of the rear wheel differential mechanism; and a transmission case accommodating the speed changer device, the forward/reverse switchover device, the rear wheel differential mechanism and the gear transmission mechanism; wherein the transmission case includes a front case portion which accommodates the speed changer device and a rear case portion which accommodates the forward/reverse switchover device, the rear wheel differential mechanism and the gear transmission mechanism, with the front case portion and the rear case portion being separable from each other; characterized in that: the gear transmission mechanism is detachably attached to a portion of inside of the transmission case which portion corresponds to a front end portion of the rear case portion; and the rear case portion is separable into the front end portion of the rear case portion and another portion of the rear case portion than the front end portion. the gear transmission mechanism is detachably attached to a portion of inside of the transmission case which portion corresponds to a front end portion of the rear case portion; and the rear case portion is separable into the front end portion of the rear case portion and another portion of the rear case portion than the front end portion.