To provide a gas insulation transformer wherein a required space in the height direction is small and site workability and safety can be improved.

The main body of a transformer is housed in a main tank 1 together with insulation cooling medium. Two coolers 4 and two blowers 5 are installed outside each of the main tanks 1, and connected with the main tank 1 through individual pipes 6 for coolers. Three main tanks 1 are arranged on a line in the longitudinal direction. The part between the respective main tanks 1 is connected by using lead connection ducts 10 which are installed on the facing side surfaces. A tap lead which connects winding with an on-load tap changer 8 and a medium-voltage lead and a low-voltage lead which connect winding with medium-voltage system and low-voltage system are arranged in a dead space 9 in the main tank 1. These lead wires are housed in the lead connection ducts 10, and mutually connected. An extension tank 8 of the on-load tap changer is arranged in the vicinity of one main tank 1.