A vehicle power transmission device in which an engine 61 equipped with a turbo charger 62 and a fluid coupling 2 with a lockup clutch are combined together, wherein a timing for connecting the lockup clutch 25 is normalized to accomplish a smooth connecting during the low-speed traveling after the start. A lockup clutch control device is equipped with means for detecting the operating condition of the turbo charger 62, and the lockup clutch 25 starts to be connected at a moment before the turbo charger 62 reaches a high output state. The lockup clutch 25 is connected within a short period of time without producing a shock due to connection and the vehicle, thereafter, accelerates smoothly. A rate of change in the revolution of the engine 61 or the pressure in the intake pipe 63 is detected to detect the operating condition of the turbo charger 62.