Frame member and battery pack using frame member

The present invention provides a frame member allowing a unit battery to be positioned simply, and allowing working efficiency during the production of a battery pack to be improved. To this end, this frame member 300 is characterized by comprising: a rectangular frame body 310; protruding flat plate portions 320 extending from the outermost peripheral side surface of the rectangular frame body 310 in the thickness direction of the rectangular frame body 310; and thin-wall recessed portions 325 having a thinner wall than the wall thickness at positions having the outermost peripheral side surface of the rectangular frame body 310 when viewed in a direction facing the internal space of the rectangular frame body 310 from the external space of the frame body 310 while passing through the interior of the rectangular frame body 310. The protruding flat plate portions 320 and the thin-wall recessed portions 325 are aligned in the thickness direction of the rectangular frame body 310. A plurality of positional restriction protrusions 323 are provided on the protruding flat plate portion 320, each of the positional restriction protrusions protruding in a direction facing the internal space of the rectangular frame body 310 from the external space of the frame body 310 while passing through the interior of the rectangular frame body 310.