PURPOSE: To improve working efficiency of expanding a baglike container and filling the same with powder, grains, etc., and to automatize the work by inserting an expanding device made up of an air blowing nozzle and a balloon into the mouth of the baglike container, and by sending air to expand the same.

CONSTITUTION: In expansion of a baglike container 3, the mouth 31 thereof is fitted to an expanding device so that the device can be kept being inserted into the mouth 31, a valve 6 is closed, and air is sent to a balloon 2 and a blowing nozzle 1, then the balloon 2 is inflated by air pressure, making its periphery stuck fast to the mouth 31, and the mouth 31 is closed therewith. Then the air is blown through the nozzle 1 into the baglike container 3 of which mouth 31 is closed, and thereby the baglike container 3 is expanded. The valve 6 is then opened, and thereby powder, grains, etc., are dropped into the baglike container 3 for filling.