An actual gear ratio change amount (ΔGr) is calculated by subtracting a pre-shift gear ratio (Gb) from an actual gear ratio (Gr). A gear ratio (G) is calculated by multiplying the actual gear ratio change amount (ΔGr) by a predetermined coefficient (C) and adding the product value to the pre-shift gear ratio (Gb). When the shift is an upshift, the gear ratio (G) is compared with aa target gear shift ratio (Ga), and the greater value is set as a virtual gear ratio (Gv). When the shift is a downshift, then the gear ratio (G) is compared with the target gear ratio (Ga) and the smaller value is set as the virtual gear ratio (Gv). A virtual input shaft rotational speed (Nv) is calculated by first dividing the actual gear ratio (Gr) by the virtual gear ratio (Gv) to obtain a quotient and by dividing the actual input shift rotational speed (Nr) by that quotient. A slip amount (S) is calculated by subtracting the actual input shaft rotational speed (Nr) of the automatic transmission (3) from the engine rotational speed (Ne). Finally, the engine rotational speed for display (Nd) is calculated by adding the slip amount (S) to the virtual input shaft rotational speed (Nv).