An endless-track traveling apparatus comprising: a first pulley and a second pulley that are arranged in such a way that the respective center axes thereof are in parallel with each other; a motor that drives at least one of the first pulley and the second pulley; and an endless track that is wound over an outer circumferential surface of the first pulley and an outer circumferential surface of the second pulley, that is driven by the at least one of the pulleys rotated by being driven by the motor, and that travels over the first pulley and the second pulley, wherein an outer circumferential surface of the endless track is configured such that it makes contact with a traveling subject so that based on the travel of the endless track, the endless-track traveling apparatus travels on the traveling subject, wherein there is provided a planar member that is disposed in a space surrounded by the endless track and has a flat portion that makes contact with an inner circumferential surface of at least one of two portions, of the endless track existing between the first pulley and the second pulley, that face each other, wherein the flat portion of the planar member makes contact with the inner circumferential surface of the endless track at a position at the traveling subject side with respect to a virtual straight line that connects a vertex, at the traveling subject side, in the outer circumferential surface (33a1) of the first pulley and a vertex, at the traveling subject side, in the outer circumferential surface (33b1) of the second pulley, wherein at least part of the outer circumferential surface, of the endless track, that faces the inner circumferential surface being in contact with the flat portion of the planar member is configured such that it makes contact with the traveling subject, characterized in that the endless track is formed in such a way that the hardness of the inner circumferential surface is larger than the hardness of the outer circumferential surface. a first pulley and a second pulley that are arranged in such a way that the respective center axes thereof are in parallel with each other; a motor that drives at least one of the first pulley and the second pulley; and an endless track that is wound over an outer circumferential surface of the first pulley and an outer circumferential surface of the second pulley, that is driven by the at least one of the pulleys rotated by being driven by the motor, and that travels over the first pulley and the second pulley, wherein there is provided a planar member that is disposed in a space surrounded by the endless track and has a flat portion that makes contact with an inner circumferential surface of at least one of two portions, of the endless track existing between the first pulley and the second pulley, that face each other, wherein the flat portion of the planar member makes contact with the inner circumferential surface of the endless track at a position at the traveling subject side with respect to a virtual straight line that connects a vertex, at the traveling subject side, in the outer circumferential surface (33a1) of the first pulley and a vertex, at the traveling subject side, in the outer circumferential surface (33b1) of the second pulley, wherein at least part of the outer circumferential surface, of the endless track, that faces the inner circumferential surface being in contact with the flat portion of the planar member is configured such that it makes contact with the traveling subject, characterized in that the endless track is formed in such a way that the hardness of the inner circumferential surface is larger than the hardness of the outer circumferential surface.