A battery module includes: a cell assembly including at least one battery cell; a module case accommodating the cell assembly; and a module connector mounted outside the module case, electrically connected to the cell assembly, and configured to connect to an external connector outside the module case. A coupling surface of the module connecter may have a first fastening part opened in at least one direction, and a corresponding coupling surface outside the module case may have a second fastening part opened bidirectionally so as to be inserted into the first fastening part in a first direction or in a second direction opposite thereto.