A mold for manufacturing a hollow composite material structure, the mold being located in the hollow composite material structure, the mold comprising: a plurality of segments (20, 30, 40) including side surfaces (23, 33) configured to be coupled to each other, each of seal grooves (25, 25a, 25b) being provided on at least one of the adjacent side surfaces (23, 33) of the segments; and a pair of annular holding members configured to fix both respective end surfaces of the segments,,, wherein: the segments are kept as a single structure by coupling the side surfaces (23, 33) of the segments to each other and fixing the end surfaces of the segments to the annular holding members; the mold further includes seal members (26, 26a, 26b) each configured to seal between the segments when the side surfaces of the segments are coupled to each other with the seal member inserted in the seal groove (25, 25a, 25b); each of the seal members is formed in a line shape having ends; 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; a lip portion is provided at the seal upper portion such that at least a tip end of the lip portion projects to an outside of the seal groove when the seal member is inserted in the seal groove; 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 are coupled to each other, the seal member is crushed in a cross sectional direction by the other of the adjacent side surfaces (23, 33) of the segments. a plurality of segments (20, 30, 40) including side surfaces (23, 33) configured to be coupled to each other, each of seal grooves (25, 25a, 25b) being provided on at least one of the adjacent side surfaces (23, 33) of the segments; and a pair of annular holding members configured to fix both respective end surfaces of the segments,,, wherein: the segments are kept as a single structure by coupling the side surfaces (23, 33) of the segments to each other and fixing the end surfaces of the segments to the annular holding members; the mold further includes seal members (26, 26a, 26b) each configured to seal between the segments when the side surfaces of the segments are coupled to each other with the seal member inserted in the seal groove (25, 25a, 25b); each of the seal members is formed in a line shape having ends; 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; a lip portion is provided at the seal upper portion such that at least a tip end of the lip portion projects to an outside of the seal groove when the seal member is inserted in the seal groove; 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 are coupled to each other, the seal member is crushed in a cross sectional direction by the other of the adjacent side surfaces (23, 33) of the segments. the segments are kept as a single structure by coupling the side surfaces (23, 33) of the segments to each other and fixing the end surfaces of the segments to the annular holding members; the mold further includes seal members (26, 26a, 26b) each configured to seal between the segments when the side surfaces of the segments are coupled to each other with the seal member inserted in the seal groove (25, 25a, 25b); each of the seal members is formed in a line shape having ends; 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; a lip portion is provided at the seal upper portion such that at least a tip end of the lip portion projects to an outside of the seal groove when the seal member is inserted in the seal groove; 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 are coupled to each other, the seal member is crushed in a cross sectional direction by the other of the adjacent side surfaces (23, 33) of the segments.