A free-standing liner unit (1) is formed by integrating a planar outer tank liner plate (2), a planar secondary barrier plate (3), and a cold insulator layer (4) that is interposed between the outer tank liner plate (2) and the secondary barrier plate (3) into a single unit. According to this free-standing liner unit (1), when building a tank, it is possible to shorten the construction period by performing the formation of the outer tank shell plates and the formation of the tank internal structure concurrently with each other, and to achieve an improvement in the handleability of the free-standing liner unit (1).