A fluid processing apparatus having a plurality of processing spaces (S) includes a plurality of containers (B) juxtaposed in a direction to each other forming processing spaces (S) respectively therein. Pressing means (H) is provided for pressing the containers (B) as juxtaposed from opposed sides thereof in the juxtaposing direction of the containers. Each container (B) includes a pair of container-forming members (41a) disposed in the juxtaposing direction and having peripheral portions thereofjoined and welded to each other. At least one of the pair of container-forming members (41a) is in the form of a dish-like member having a peripheral portion used as a joining margin and a bulging central portion.