An automatic gear shifting control device of a vehicle comprising: a control part for executing an automatic gear shifting operation of a transmission in response to at least vehicle-speed information; a first sensor for detecting a rotational speed of a front wheel; a second sensor for detecting a rotational speed of a rear wheel driven by an engine of the vehicle; and a rotational-speed-difference detection means for detecting the difference in rotational speed between the front wheel and the rear wheel based on information from the first sensor and information from the second sensor, wherein the control part is configured to execute an automatic gear shifting control in response to the vehicle-speed information calculated based on the larger rotational speed out of the rotational speed of the front wheel and the rotational speed of the rear wheel when the difference in rotational speed between the front wheel and the rear wheel is detected; wherein the control part executes a gear shifting operation of the transmission toward a shift-up side when the difference in rotational speed is continuously detected for a predetermined time or more; wherein the control part is configured to execute an automatic gear shifting control in response to the vehicle-speed information calculated based on the larger rotational speed out of the rotational speed of the front wheel and the rotational speed of the rear wheel when the difference in rotational speed is detected at the time of deceleration of the vehicle speed; and characterised in that when the difference in rotational speed is detected between the front and rear wheels, an instruction for executing the automatic gear shifting in response to the larger rotational speed is transmitted to the gear shifting control instruction part by a reference wheel change means, a value of the difference in rotational speed which allows the reference wheel change means to output the changing instruction is increased or decreased in response to the value of the larger rotational speed. a control part for executing an automatic gear shifting operation of a transmission in response to at least vehicle-speed information; a first sensor for detecting a rotational speed of a front wheel; a second sensor for detecting a rotational speed of a rear wheel driven by an engine of the vehicle; and a rotational-speed-difference detection means for detecting the difference in rotational speed between the front wheel and the rear wheel based on information from the first sensor and information from the second sensor, wherein the control part is configured to execute an automatic gear shifting control in response to the vehicle-speed information calculated based on the larger rotational speed out of the rotational speed of the front wheel and the rotational speed of the rear wheel when the difference in rotational speed between the front wheel and the rear wheel is detected; wherein the control part executes a gear shifting operation of the transmission toward a shift-up side when the difference in rotational speed is continuously detected for a predetermined time or more; wherein the control part is configured to execute an automatic gear shifting control in response to the vehicle-speed information calculated based on the larger rotational speed out of the rotational speed of the front wheel and the rotational speed of the rear wheel when the difference in rotational speed is detected at the time of deceleration of the vehicle speed; and characterised in that when the difference in rotational speed is detected between the front and rear wheels, an instruction for executing the automatic gear shifting in response to the larger rotational speed is transmitted to the gear shifting control instruction part by a reference wheel change means, a value of the difference in rotational speed which allows the reference wheel change means to output the changing instruction is increased or decreased in response to the value of the larger rotational speed.