A composite material molding jig for molding a long member made of a fiber base material and a resin on a plate member includes: a first member that is made of a material having a thermal expansion coefficient equivalent to a thermal expansion coefficient of the long member, internally includes a space serving as a mold of the long member, and has an outer surface formed flat in a longitudinal direction; and a second member that is made of a material lighter than the material of the first member, internally includes a space shaped to contain the first member, and has an inner surface formed flat in the longitudinal direction, wherein the fiber base material is placed in the space inside the first member, and the first member is placed in the space inside the second member for molding the long member.