Provided is a method for manufacturing a tank and a manufacturing device thereof that can achieve resin impregnation within a short time. The method wraps fibers in an overlapping manner in a radial direction around an outer surface of a liner such that a first fiber layer (braiding layer) on an outer surface of a dome portion is less dense than a second fiber layer (helical layer) on an outer surface of a straight body portion and such that a portion of a lamina of the first fiber layer, which is less dense, is interposed continuously from the first fiber layer partially between laminae of the second fiber layer, and then impregnates the fiber layer including the first fiber layer and the second fiber layer with a resin.