A battery monitoring unit includes a plurality of voltage detection lines, a flexible printed circuit board extending in a stuck direction of single batteries, an electronic circuit connected to one end portions of the plurality of the voltage detection lines so as to detect voltage of each of the single batteries and mounted on the flexible printed circuit board, a plurality of busbar fixing portions formed integrally with the flexible printed circuit board and to which the plurality of the busbars are fixed respectively, and communication lines disposed in the flexible printed circuit board so as to connect between the electronic circuit and a battery ECU.