A hybrid transmission for a hybrid vehicle mounting thereon an engine and a pair of electric motor/generators operates in a plurality of driving modes including EV mode in which the vehicle is powered by only the pair of motor/generators and EIVT mode in which the vehicle is powered by both the pair of motor/generators and the engine. The driving mode is shifted continuously and smoothly through a mode-shift transition process, in which the operating state is regulated to decrease the relative torque and/or the relative rotational speed between the contact elements of an engine clutch before engaging or disengaging the engine clutch.