Abstract: An apparatus for filling electric apparatus such as transformers with insulating oil consists of first and second decompression tanks each having an opening at one side for taking the transformers in and out of each tank. The tanks are placed so that the openings are opposed to each other. A flatcar is provided between the openings of the tanks and reciprocally moved in the direction in which the openings of the tanks are opposed to each other. A door is provided on the flatcar. The openings of the tanks are alternately closed by the door when the flatcar is reciprocally moved. Two carriers for carrying the transformers are provided on respective sides of the door. The transformers carried on the carriers are alternately taken in and out of the tanks when the flatcar is reciprocally moved. The apparatus further includes a vacuum pump for decompressing each tank. The transformers are filled with insulating oil in the tanks under decompressed condition.