A non-pneumatic tire assembly comprising: an attachment body attachable to an axle; an inner tubular body fitted onto the attachment body from the outside; an outer tubular body configured to surround the inner tubular body from the outside in a tire radial direction; and a plurality of connecting members disposed between the inner tubular body and the outer tubular body in a tire circumferential direction and configured to connect both of the tubular bodies (12, 13) while maintaining relative elastic displacement therebetween, an outer circumferential section of the attachment body that is locked to an inner circumferential section of the inner tubular body is inclined throughout the circumference in the tire circumferential direction from the outside toward the inside in the tire radial direction as it goes from both of the outsides toward the inside in a tire width direction, and formed in a V shape when seen in a cross-sectional view in the tire width direction, and the attachment body comprises a pair of split bodies (25, 26) that are split in the tire width direction, characterised in that: the inner tubular body, the outer tubular body and the plurality of connecting members are integrally formed of a synthetic resin material, a plurality of key groove sections recessed inward in the tire radial direction and extending in the tire width direction are formed at outer circumferential surfaces of outer ring sections of the split bodies (25, 26) at intervals in the tire circumferential direction, the key groove sections being opened only at the inside of both ends in the tire width direction and closed at the outside in the outer circumferential surfaces of the outer ring sections, among wall surfaces that define the key groove sections, pairs of side wall surfaces and bottom wall surfaces that are opposite to each other in the tire circumferential direction form right angles, protrusion sections of the inner tubular body are fitted into the key groove sections, among outer surfaces of the protrusion sections, pairs of side wall surfaces standing up from the inner circumferential surface of the inner tubular body and top wall surfaces directed inward in the tire radial direction form right angles, and sizes in the tire circumferential direction of the protrusion sections and the key groove sections are equal to each other. an attachment body attachable to an axle; an inner tubular body fitted onto the attachment body from the outside; an outer tubular body configured to surround the inner tubular body from the outside in a tire radial direction; and a plurality of connecting members disposed between the inner tubular body and the outer tubular body in a tire circumferential direction and configured to connect both of the tubular bodies (12, 13) while maintaining relative elastic displacement therebetween, an outer circumferential section of the attachment body that is locked to an inner circumferential section of the inner tubular body is inclined throughout the circumference in the tire circumferential direction from the outside toward the inside in the tire radial direction as it goes from both of the outsides toward the inside in a tire width direction, and formed in a V shape when seen in a cross-sectional view in the tire width direction, and characterised in that: the inner tubular body, the outer tubular body and the plurality of connecting members are integrally formed of a synthetic resin material, a plurality of key groove sections recessed inward in the tire radial direction and extending in the tire width direction are formed at outer circumferential surfaces of outer ring sections of the split bodies (25, 26) at intervals in the tire circumferential direction, the key groove sections being opened only at the inside of both ends in the tire width direction and closed at the outside in the outer circumferential surfaces of the outer ring sections, among wall surfaces that define the key groove sections, pairs of side wall surfaces and bottom wall surfaces that are opposite to each other in the tire circumferential direction form right angles, protrusion sections of the inner tubular body are fitted into the key groove sections, among outer surfaces of the protrusion sections, pairs of side wall surfaces standing up from the inner circumferential surface of the inner tubular body and top wall surfaces directed inward in the tire radial direction form right angles, and sizes in the tire circumferential direction of the protrusion sections and the key groove sections are equal to each other.