To enable engagement of a hydraulic clutch while shock is reduced without releasing lockup of a torque converter.

A jedgement that a clutch engagement will cause a shock is passed if the car speed (v) is below the specified value v0 (S2) during the engaging motion of a hydraulic clutch (S1), or the car speed (v) is the specified value v0 or over while the lockup condition is generated and the absolute Ne-Ni of the difference in the revolving speed between the input and output shafts is the specified value No or over (S2-S4). A clutch solenoid valve to supply a working oil to the actuator of the hydraulic clutch is on-off controlled with a prescribed frequency N so that the pressure of the working oil supplied to the actuator rises gradually (S5). This puts the hydraulic clutch in so-called partial clutch engagement condition, and the shock is reduced.