PROBLEM TO BE SOLVED: To provide a culturing bag by which a space for growing mushrooms on a medium can be secured. SOLUTION: The mouth 1B of a bag opened in the right and left direction at the upper part of a bag body 1 in a nearly box shape in which the culture medium A is stored is closed. The back part 8 of the bag is formed into a ridge shape at the back surface 3 of the closed mouth 1B of the bag. Both right and left side parts of the back part 8 of the bag are folded backward and fixed to the back part 8 of the bag. The mouth 1B side of the bag is supported at a high position by supporting the back part 8 of the bag by both the right and left side parts to enable the space 1C for the growing to be secured. The apparatus has a freely lifted and lowered nipping part for nipping the folded part 1D (the mouth 1B of the bag) side, folding bodies arranged at both outer sides of the nipping part for forming an openable space, and a welding means of a device for welding both the right and left side parts of the folded part 1D (the mouth 1B of the bag) folded by the folding bodies.
