A blanket installation method includes: a transporting step of transporting a blanket unit (1), in which a blanket (2) and a transport jig (3) are integrally coupled, between an inner tank (60) and an outer tank (50) of a double shell structure tank in a suspended condition; and a mounting step of mounting the blanket unit (1) on a shell plate of the inner tank (60). The transport jig (3) is formed by attaching a blanket fixing pin (34) to a jig main body (3A) through pin coupling. The blanket (2) is held at the blanket fixing pin (34).