generator torques tm 1 tm 2 controls the torques of motor generators mg 1 mg 2 so that the target torques are attained the control executed by integrated controller 9 at start of engine 2 during motor running in which the vehicle is driven by the power of motor generators mg 1 mg 2 only is classified by functions and shown in the block diagram of fig3 in this instance integrated controller 9 includes clutch engagement force determining section 9 a and engine start instruction determining section 9 b clutch engagement force determining section 9 a starts motion at the moment t 1 of fig4 a i e the moment at which a running mode is changed for the necessity of the power of engine 2 during motor running and gradually increases target clutch engagement force tc from zero at a predetermined time gradient as shown in fig4 a clutch controller 7 supplies clutch engagement oil pressure pc for realizing target clutch engagement force tc to clutch 3 thereby increasing the engagement force of clutch 3 gradually such gradual increase of the clutch engagement force causes engine 2 to be cranked and therefore engine speed ne to increase as shown in fig4 a at the moment t 2 of fig4 a at which engine speed ne arrives at startable speed nig clutch engagement force determining section 9 a holds target clutch engagement force tc at the value caused at the moment t 2 and inhibits the engagement force of clutch 3 from increasing further clutch engagement force determining section 9 a simultaneously at the moment t 2 supplies to engine start instruction determining section.