A membrane cartridge in an immersion type membrane separation apparatus capable of suppressing vibrations applied to the membrane cartridge by an ascending force of membrane cleaning gas and others by firmly coupling the adjacent membrane cartridges disposed in parallel. In a membrane cartridge in an immersion type membrane separation apparatus, selvages larger in thickness than a membrane cartridge main body are formed at both sides of the membrane cartridge, and a header forming part is formed on one selvage, and a guide hole is formed in other selvage relatively, and the header forming part and the guide hole of the membrane cartridge disposed adjacently by varying the direction mutually are formed to communicate and connect with each other.