The first plate P1 may include the first boundary portion P1a coupled to the main boundary portion M and the first exposure portion P1b exposed from the main boundary portion M. Here, the first exposure portion P1b may be exposed from the main boundary portion M and may be exposed to the accommodation space G surrounded by the main boundary portion M. As described below, the first exposure portion P1b may be exposed through the accommodation space G and may form the cooling fluid passage F for cooling the cell assembly B accommodated in the accommodation space G. That is, the first boundary portion P1a of the first plate P1 may form the coupling with the main boundary portion M, and the first exposure portion P1b of the first plate P1 may extend to deviate from the main boundary portion M and may form the cooling fluid passage F of the accommodation space G (the cell assembly B accommodated in the accommodation space G) surrounded by the main boundary portion M. As described below, the cooling fluid passage F may be formed between the first plate P1 forming the bottom of the accommodation space G and the second plate P2 arranged to face the first plate P1, and the first plate P1 may mediate a heat transfer between the lower surface of the cell assembly B and the cooling fluid passage F and may refrigerate the cell assembly B. According to some embodiments, the first plate P1 may include a metal material having excellent heat conductivity, for example, aluminum, to facilitate a heat transfer between the cell assembly B and the cooling fluid passage F. According to some embodiments, the first plate P1 may include a metal material that is different from a resin material forming the main housing, and the first plate P1 may be integrally formed with the main housing H via insert molding. Here, the first plate P1 may be separately formed for each of the plurality of accommodation spaces G. The first plate P1 may be separately formed for each of the adjacent accommodation spaces G, and thus, thermal interference or electrical interference between different cell assemblies B accommodated in the adjacent accommodation spaces G may be prevented or reduced. As described above, the first plate P1 separately formed for each of the plurality of accommodation spaces G may form the supporting base of the cell assembly B accommodated in each accommodation space G, and the location of the first plate P1 may be firmly fixed by the first coupling line L1 surrounding each accommodation space G. For example, the first coupling line L1 may be formed to have a shape of a closed loop surrounding each accommodation space G.