To provide a blowing-in type gas sealing sheet for automatically opening a gas entrance port.

Gas having entered into a gas filling port inflates an air injection channel 9, opens two outer films 2a and 2b by being pulled outward in the longitudinal direction, tensions the films in the lateral direction, presses two inner films 1a and 1b by a plurality of heat seal blocks 5, opens a place of applying a heat resistant material of the two inner films 1a and 1b by being pulled outward in the longitudinal direction, opens the two inner films 1a and 1b by being pulled outward in the longitudinal direction by a plurality of third parts accompanying the two outer films 2a and 2b, and opens a gas entrance port, and an air chamber is blocked up by pressing the second side edge of the two inner films 1a and 1b after the gas enters the air chamber.