A mold for manufacturing a hollow composite material structure, the mold having a seal structure being located in the hollow composite material structure, being constituted by a plurality of segments (20, 30), and being kept as a single structure by coupling adjacent side surfaces (23, 33) of the segments (20, 30) to each other, the seal structure being provided at the adjacent side surfaces (23, 33) of the segments (20, 30), the seal structure comprising: seal grooves each provided on at least one of the adjacent side surfaces (23, 33) of the segments (20, 30); and seal members each formed in a line shape having ends and inserted in the seal groove to seal between the segments (20, 30) by coupling the adjacent side surfaces (23, 33) of the segments (20, 30) to each other, wherein: a part of the seal member which part contacts a bottom surface of the seal groove when the seal member is inserted in the seal groove is referred to as a seal bottom portion; a part of the seal member which part is opposed to the seal bottom portion is referred to as a seal upper portion; the seal member is hollow therein or includes a concave portion on at least the seal bottom portion of the seal member; and when the adjacent side surfaces (23, 33) of the segments (20, 30) are coupled to each other, the seal member is crushed in a cross sectional direction by the other of the adjacent side surfaces (33, 23) of the segments (20, 30), a lip portion (262, 265) is provided at the seal upper portion such that at least a tip end of the lip portion (262, 265) projects to an outside of the seal groove when the seal member is inserted in the seal groove; characterized in that a surface of the segment (20, 30) which surface constitutes an outer peripheral surface of the single structure is referred to as a front surface of the segment (20, 30); both end portions of the seal groove are bent toward the front surface of the segment (20, 30); and when the seal member is inserted in the seal groove, both end portions of the seal member are pressed by respective end portion pressing members, provided on the front surface of the segment (20, 30), so as not to be exposed from the front surface of the segment (20, 30). seal grooves each provided on at least one of the adjacent side surfaces (23, 33) of the segments (20, 30); and seal members each formed in a line shape having ends and inserted in the seal groove to seal between the segments (20, 30) by coupling the adjacent side surfaces (23, 33) of the segments (20, 30) to each other, wherein: a part of the seal member which part contacts a bottom surface of the seal groove when the seal member is inserted in the seal groove is referred to as a seal bottom portion; a part of the seal member which part is opposed to the seal bottom portion is referred to as a seal upper portion; the seal member is hollow therein or includes a concave portion on at least the seal bottom portion of the seal member; and when the adjacent side surfaces (23, 33) of the segments (20, 30) are coupled to each other, the seal member is crushed in a cross sectional direction by the other of the adjacent side surfaces (33, 23) of the segments (20, 30), a lip portion (262, 265) is provided at the seal upper portion such that at least a tip end of the lip portion (262, 265) projects to an outside of the seal groove when the seal member is inserted in the seal groove; characterized in that a surface of the segment (20, 30) which surface constitutes an outer peripheral surface of the single structure is referred to as a front surface of the segment (20, 30); both end portions of the seal groove are bent toward the front surface of the segment (20, 30); and when the seal member is inserted in the seal groove, both end portions of the seal member are pressed by respective end portion pressing members, provided on the front surface of the segment (20, 30), so as not to be exposed from the front surface of the segment (20, 30). a part of the seal member which part contacts a bottom surface of the seal groove when the seal member is inserted in the seal groove is referred to as a seal bottom portion; a part of the seal member which part is opposed to the seal bottom portion is referred to as a seal upper portion; the seal member is hollow therein or includes a concave portion on at least the seal bottom portion of the seal member; and when the adjacent side surfaces (23, 33) of the segments (20, 30) are coupled to each other, the seal member is crushed in a cross sectional direction by the other of the adjacent side surfaces (33, 23) of the segments (20, 30), a lip portion (262, 265) is provided at the seal upper portion such that at least a tip end of the lip portion (262, 265) projects to an outside of the seal groove when the seal member is inserted in the seal groove; characterized in that a surface of the segment (20, 30) which surface constitutes an outer peripheral surface of the single structure is referred to as a front surface of the segment (20, 30); both end portions of the seal groove are bent toward the front surface of the segment (20, 30); and when the seal member is inserted in the seal groove, both end portions of the seal member are pressed by respective end portion pressing members, provided on the front surface of the segment (20, 30), so as not to be exposed from the front surface of the segment (20, 30).