Provided is a battery pack of a module having a plurality of cells connected in series. In this module, terminals for external connections are in an identical direction, thereby to make no wiring across the module. The battery pack is enabled to improve the workability and to reduce the connection mistakes by making only the connections of bus bars between units at the module creating time. Three flat cells (2a - 2c) are arranged in parallel to constitute a three-piece unit (1), and an anode terminal (3) and a cathode terminal (4) are disposed in the upper portions of the individual cells (2a - 2c). The cathode terminal (4) of the first cell (2a) and the anode terminal (3) of the second cell (2b) are connected by a first bus bar (5) arranged obliquely, and the cathode terminal (4) of the second cell (2b) and the anode terminal (3) of the third cell (2c) are connected by a second bus bar (6) arranged in a direction perpendicular to the longitudinal direction of the cells. The two flat cells (12a and 12b) are arranged in parallel to constitute a two-piece unit (11), and the anode terminal (13) and the cathode terminal (14) of the individual cells (12a and 12b) are connected by a second bus bar (16).