A synthetic resin-made multilayer bottle comprising: a synthetic resin-made outer shell bottle which has a cylindrical outer opening section, a shoulder section continuing from the outer opening section, a body section continuing from the shoulder section, and a bottom section continuing from the body section, and which can restore an original shape thereof with respect to an external pressure; a synthetic resin-made inner container body which has a cylindrical inner opening section provided inside the outer opening section of the outer shell bottle, and an inner container main body which continues from the inner opening section, which is shaped along an inner surface shape of the outer shell bottle, and which deforms in response to an external pressure; and an air passage which is formed between the outer opening section and the inner opening section and which introduces outside air between the outer shell bottle and the inner container body, wherein an upper end contact part that is in contact with the inner circumferential surface of the outer opening section is provided on at least a part of an upper end outer circumferential surface of the inner opening section, wherein a lower end contact part that is in contact with the inner circumferential surface of the outer opening section is provided on at least a part of a lower end outer circumferential surface of the inner opening section, and wherein a separated section is provided between the outer circumferential surface of the inner opening section and the inner circumferential surface of the outer opening section, thereby spacing the separated section farther inward than the air passage of the upper end contact part in a radial direction with respect to the inner circumferential surface of the outer opening section, characterized in that a small-diameter section having a diameter that is smaller than an inner diameter of an open end of the inner opening section is provided on an inner circumferential surface of the inner opening section, wherein the separated section is positioned in an area corresponding to the small-diameter section, said separated section thereby forming a hollow space between the outer circumferential surface of the inner opening section and the inner circumferential surface of the outer opening section. a synthetic resin-made outer shell bottle which has a cylindrical outer opening section, a shoulder section continuing from the outer opening section, a body section continuing from the shoulder section, and a bottom section continuing from the body section, and which can restore an original shape thereof with respect to an external pressure; a synthetic resin-made inner container body which has a cylindrical inner opening section provided inside the outer opening section of the outer shell bottle, and an inner container main body which continues from the inner opening section, which is shaped along an inner surface shape of the outer shell bottle, and which deforms in response to an external pressure; and an air passage which is formed between the outer opening section and the inner opening section and which introduces outside air between the outer shell bottle and the inner container body, wherein an upper end contact part that is in contact with the inner circumferential surface of the outer opening section is provided on at least a part of an upper end outer circumferential surface of the inner opening section, wherein a lower end contact part that is in contact with the inner circumferential surface of the outer opening section is provided on at least a part of a lower end outer circumferential surface of the inner opening section, and wherein a separated section is provided between the outer circumferential surface of the inner opening section and the inner circumferential surface of the outer opening section, thereby spacing the separated section farther inward than the air passage of the upper end contact part in a radial direction with respect to the inner circumferential surface of the outer opening section, characterized in that a small-diameter section having a diameter that is smaller than an inner diameter of an open end of the inner opening section is provided on an inner circumferential surface of the inner opening section, wherein the separated section is positioned in an area corresponding to the small-diameter section, said separated section thereby forming a hollow space between the outer circumferential surface of the inner opening section and the inner circumferential surface of the outer opening section.