To judge a half-engaged-clutch state even while a vehicle is stopped, in the vehicle provided with a manual transmission that is connected with an output side of an engine via a clutch.

When an engine rotation number is decreased while the vehicle is stopped, a high frequency component and a low frequency component of the engine rotation number are extracted with an annealing treatment and a locus length of the high frequency component and a locus length of the low frequency component are calculated by integrating the extracted high frequency component and low frequency component and then whether it is in the half-engaged-clutch state or not is judged from relation of the calculated locus length of the high frequency component and the locus length of the low frequency component. For example, a two-dimensional map (Fig. 5) in which a half-engaged-clutch judgement area is set using the locus length of the high frequency component and the locus length of the low frequency component as parameters is used and the locus length of the high frequency component and the locus length of the low frequency component are plotted on the two-dimensional map and whether it is in the half-engaged-clutch state or not is judged depending on whether the plot points are in the half-engaged-clutch judgement area or not.