A battery pack, comprising: a plurality of bare cells electrically connected to one another; and a housing that accommodates the bare cells therein, the housing including a frame portion (120; 220; 320) and a pair of side portions (110; 210; 310) respectively connected to a first end and a second end of the frame portion (120; 220; 320), wherein the housing includes a guide portion (150; 250; 350) to guide a flow of fluid, the guide portion (150; 250; 350) being located where the first end of the frame portion (120; 220; 320) and one said side portion (110; 210; 310) are adjacent to each other, the frame portion (120; 220; 320) includes a pair of first frame portions that face each other in a first direction, and a second frame portion (122; 321; 322) that connects bottoms of the pair of first frames, the side portions (110; 210; 310) face each other in a second direction perpendicular to the first direction at the first end (151; 251) and the second end of the frame portion (120; 220; 320), the one said side portion (110; 210; 310) includes a base portion (111; 211; 311) that vertically contacts the first end (151; 251) of the frame portion (120; 220; 320), and a flange portion (112; 212; 312) protrudes toward the frame portion (120; 220; 320) from the base portion (111; 211; 311), characterized in that the flange portion (112; 212; 312) is insertably coupled to an inside of the frame portion (120; 220; 320) to overlap with the frame portion (120; 220; 320), and the guide portion (150; 250; 350) is located where the side portion (110; 210; 310) and the frame portion (120; 220; 320) overlap with each other. a plurality of bare cells electrically connected to one another; and a housing that accommodates the bare cells therein, the housing including a frame portion (120; 220; 320) and a pair of side portions (110; 210; 310) respectively connected to a first end and a second end of the frame portion (120; 220; 320), wherein the housing includes a guide portion (150; 250; 350) to guide a flow of fluid, the guide portion (150; 250; 350) being located where the first end of the frame portion (120; 220; 320) and one said side portion (110; 210; 310) are adjacent to each other, the frame portion (120; 220; 320) includes a pair of first frame portions that face each other in a first direction, and a second frame portion (122; 321; 322) that connects bottoms of the pair of first frames, the side portions (110; 210; 310) face each other in a second direction perpendicular to the first direction at the first end (151; 251) and the second end of the frame portion (120; 220; 320), the one said side portion (110; 210; 310) includes a base portion (111; 211; 311) that vertically contacts the first end (151; 251) of the frame portion (120; 220; 320), and a flange portion (112; 212; 312) protrudes toward the frame portion (120; 220; 320) from the base portion (111; 211; 311), characterized in that the flange portion (112; 212; 312) is insertably coupled to an inside of the frame portion (120; 220; 320) to overlap with the frame portion (120; 220; 320), and the guide portion (150; 250; 350) is located where the side portion (110; 210; 310) and the frame portion (120; 220; 320) overlap with each other.