To make an advancing state to a gear shift of a gear shift stage easy to be visualized during a traveling by displaying the gear shift stage of a traveling vehicle according to a prescribed signal corresponding to a position of the gear shift stage of the traveling vehicle when a solenoid valve is turned on/off by a control signal.

When a driver operates a gear shift lever and runs a vehicle by an arbitrary traveling stage, a target gear shift stage is determined from speed and throttle opening by a control part 200 and gear shift control signals, that is, signals for controlling a gear shift control valve are outputted from solenoid So1-A, B terminals. The signals are impressed on gates of field effect transistors FG1, FG2 via resistances R1, R5 in an interface circuit 300 and signals impressed from a voltage supply part 100 are impressed on each solenoid valve L1, L2. A programmable logic device PDL is controlled via transistors Q1, Q2 and a gear shift display signal is outputted to a gear shift stage display part 400.