PURPOSE: To prevent the continuous execution of a downshift and a upshift by, when the downshift has been judged on the second speed change diagram based on the quantity of pressing downup an accel pedal and car speed, prohibiting the upshift on the first speed change diagram based on the quantity of intake air and the car speed until a fixed time elapses.

CONSTITUTION: The first speed change diagram shown by a full line is formed of a speed change line based on the quantity of intake air per unit revolution and car speed, and previously stored in an electronic control device for speed change. The second speed change diagram shown by a dashed line is similarly formed on the quantity of pressing downofan accel pedal and the car speed an stored. When a TA downshift judging means judges that the downshift is based on the second speed change diagram, an upshift prohibiting means sends an upshift prohibiting signal until a fixed time elapses to prohibit the upshift executed by a speed change control means on the first speed change diagram.