a double clutch transmission of a vehicle is disclosed . the double clutch transmission may selectively transmit power of a power source to two input shafts through two clutches and may output changed power through two output shafts after the power selectively transmitted to the two input shafts is changed . the two input shafts may respectively have a plurality of input gears fixed thereon , the two output shafts may respectively have a plurality of speed gears rotatable on the output shafts and a plurality of synchronizers operably connecting each speed gear to any one of the output shafts , and each input gear may be engaged with at least one speed gear .