A method of manufacturing an off-center container includes: stretching a preform made of resin having a bottomed shape with a stretching rod, heating the preform; and blow-molding the off-center container, in which a central axis of a neck portion is displaced from a central axis of a body portion, by introducing a pressurized fluid into the preform disposed in a mold. The container has a flat shape and a dimension in a first direction in a cross section is longer than in a second direction perpendicular to the first direction. In a circumferential cross section of the preform, a thickness of a first region corresponding to a surface extending in the first direction of the container is set to be thicker than a thickness of a second region corresponding to a surface extending in the second direction of the container.