A composite material molding jig comprising: - a tube having flexibility; and - at least one rigid plate (6, 6A, 6B, 6C) which reinforces strength of the tube partially, wherein the tube is usable in a state where air is introduced inside the tube wherein the at least one rigid plate (6, 6A, 6B, 6C) include plates placed with at least one clearance in a direction perpendicular to a length direction of the tube, the plates being arranged such as to allow partial deformation of the tube in a cross section of the tube and suppress deformation of the tube in a plane parallel to the length direction of the tube, wherein the composite material molding jig is configured to support a composite material structure during curing, the composite material structure having an elongated structure and a panel, the elongated structure having a hat-shaped cross section, the elongated structure having a cap two webs and round-chamfered corners, the elongated structure being placed on the panel, the composite material molding jig being configured to support an inside of the elongated structure, and wherein the at least one rigid plate (6, 6A, 6B, 6C) include: - a first plate that reinforces strength of a first part of the tube, the first part being configured to support an inside of the cap of the elongated structure; and - two second plates that reinforce strength of second parts of the tube respectively, the second parts being configured to support insides of the two webs of the elongated structure respectively, wherein the rigid plates (6, 6A, 6B, 6C) are not disposed on each of the parts of the tube which are configured to fit with the round-chamfered corners of the elongated structure from the insides. - a tube having flexibility; and - at least one rigid plate (6, 6A, 6B, 6C) which reinforces strength of the tube partially, wherein the tube is usable in a state where air is introduced inside the tube wherein the at least one rigid plate (6, 6A, 6B, 6C) include plates placed with at least one clearance in a direction perpendicular to a length direction of the tube, the plates being arranged such as to allow partial deformation of the tube in a cross section of the tube and suppress deformation of the tube in a plane parallel to the length direction of the tube, wherein the composite material molding jig is configured to support a composite material structure during curing, the composite material structure having an elongated structure and a panel, the elongated structure having a hat-shaped cross section, the elongated structure having a cap two webs and round-chamfered corners, the elongated structure being placed on the panel, the composite material molding jig being configured to support an inside of the elongated structure, and wherein the at least one rigid plate (6, 6A, 6B, 6C) include: - a first plate that reinforces strength of a first part of the tube, the first part being configured to support an inside of the cap of the elongated structure; and - two second plates that reinforce strength of second parts of the tube respectively, the second parts being configured to support insides of the two webs of the elongated structure respectively, wherein the rigid plates (6, 6A, 6B, 6C) are not disposed on each of the parts of the tube which are configured to fit with the round-chamfered corners of the elongated structure from the insides. wherein the tube is usable in a state where air is introduced inside the tube wherein the at least one rigid plate (6, 6A, 6B, 6C) include plates placed with at least one clearance in a direction perpendicular to a length direction of the tube, the plates being arranged such as to allow partial deformation of the tube in a cross section of the tube and suppress deformation of the tube in a plane parallel to the length direction of the tube, wherein the composite material molding jig is configured to support a composite material structure during curing, the composite material structure having an elongated structure and a panel, the elongated structure having a hat-shaped cross section, the elongated structure having a cap two webs and round-chamfered corners, the elongated structure being placed on the panel, the composite material molding jig being configured to support an inside of the elongated structure, and wherein the at least one rigid plate (6, 6A, 6B, 6C) include: - a first plate that reinforces strength of a first part of the tube, the first part being configured to support an inside of the cap of the elongated structure; and - two second plates that reinforce strength of second parts of the tube respectively, the second parts being configured to support insides of the two webs of the elongated structure respectively, - a first plate that reinforces strength of a first part of the tube, the first part being configured to support an inside of the cap of the elongated structure; and - two second plates that reinforce strength of second parts of the tube respectively, the second parts being configured to support insides of the two webs of the elongated structure respectively, wherein the rigid plates (6, 6A, 6B, 6C) are not disposed on each of the parts of the tube which are configured to fit with the round-chamfered corners of the elongated structure from the insides.