PURPOSE: To obtain a small-sized transformer directly coupled with a cable, which requires no oil wall bushing nor spacer, by detachably connecting a cable, through a contact conductor, in a porcelain tube oil-tightly provided on the transformer body side.

CONSTITUTION: A porcelain tube 21 is oil-tightly mounted on a cable connecting box 3 by means of a mounting member 19. A connection conductor 27 is attach- ed oil-tightly penetrating an upper member 17 of the porcelain tube 21. One end of the connection conductor 27 located in the cable connecting box 3 is connected to a transformer winding 2 through a terminal 22 and a lead wire 12. On the other hand, the other end located in the porcelain tube 21 is provided with a contact conductor 28 having a resilient clamping pressure for connecting a cable. Both a transformer tank 1 and the cable connecting box 3 are vacuum-filled with an insulating oil 5.