A panel (7) is prepared by bonding an outer panel (8) and an inner panel (9). A linear reinforcement (W) is arranged between the outer panel (8) and the inner panel (9). The outer panel (8) or the inner panel (9) includes two or more fixing parts (63) for fixing the linear reinforcement (W) and at least one projection (64, 66, 72, 73) provided between the fixing parts (63). The linear reinforcement (W) is supported by the projection (64, 66, 72, 73) between the fixing parts (63) to be spaced from the outer and inner panels (8, 9) while tension is applied to the linear reinforcement (W).