A battery module has a reduced risk of secondary fire or explosion. The battery module includes at least two cell assemblies including a plurality of secondary batteries, a module housing having a gas passage on at least one of left side or right side of the cell assembly for circulation of gas generated from the cell assembly, and a flame retardant plate including a body interposed between the at least two cell assemblies, and a flame barrier extending in a left-right direction from at least one of left end or right end of the body and disposed in part of the gas passage.