A square secondary battery, comprising: a flat electrode group that is manufactured by winding positive and negative electrodes; a flat square battery can that stores the electrode group; a battery lid that seals an opening of the battery can; an insulating member that is fixed to the battery lid and stored in the battery can; and a storage member made of a bag-like insulating sheet that has a volume smaller than the battery can, and is stored in the battery can and stores the electrode group together with an electrolyte, wherein the battery lid includes a liquid injection port through which the electrolyte is injected, and includes a safety valve that is opened when an internal pressure of the battery can rises up to a predetermined value, and wherein the insulating member adheres to the battery lid to seal a space formed with respect to the battery lid, and is bonded to an opening of the storage member together to seal the opening, and wherein the electrode group is configured to wind the positive and negative electrodes (41, 42) around a winding axis perpendicular to the battery lid, and wherein the insulating member includes an annular bonding portion (3c, 3c') that is formed along an outer shape of the electrode group when viewed from a direction parallel with the winding axis, and wherein the insulating member is configured to include an opening (3b, 3b', 3e) at a position corresponding to the liquid injection port inside the annular bonding portion (3c, 3c'), and a position corresponding to the safety valve inside the annular bonding portion (3c, 3c'), and wherein the insulating member includes a rib that reinforces the opening (3b, 3b', 3e) of the insulating member. a flat electrode group that is manufactured by winding positive and negative electrodes; a flat square battery can that stores the electrode group; a battery lid that seals an opening of the battery can; an insulating member that is fixed to the battery lid and stored in the battery can; and a storage member made of a bag-like insulating sheet that has a volume smaller than the battery can, and is stored in the battery can and stores the electrode group together with an electrolyte, wherein the battery lid includes a liquid injection port through which the electrolyte is injected, and includes a safety valve that is opened when an internal pressure of the battery can rises up to a predetermined value, and wherein the insulating member adheres to the battery lid to seal a space formed with respect to the battery lid, and is bonded to an opening of the storage member together to seal the opening, and wherein the electrode group is configured to wind the positive and negative electrodes (41, 42) around a winding axis perpendicular to the battery lid, and wherein the insulating member includes an annular bonding portion (3c, 3c') that is formed along an outer shape of the electrode group when viewed from a direction parallel with the winding axis, and wherein the insulating member is configured to include an opening (3b, 3b', 3e) at a position corresponding to the liquid injection port inside the annular bonding portion (3c, 3c'), and a position corresponding to the safety valve inside the annular bonding portion (3c, 3c'), and wherein the insulating member includes a rib that reinforces the opening (3b, 3b', 3e) of the insulating member.