A shaft structure to be installed in a shaft capable of making a power-transmission, the shaft structure comprising: a male component (21; 221; 321; 421; 521; 821; 921; 1021; 1121; 1221; 1321) having a plurality of male spline parts (21c; 221c; 321c; 821c; 1221c; 1321c) and a plurality of male spline bottom parts (21d; 221d; 321d) formed on an outer peripheral part thereof; a female component (22; 222; 322; 422; 522; 822; 922; 1022; 1122; 1222; 1322) having a plurality of female spline parts (22b; 222b; 322b; 422b; 522b; 1122b) and a plurality of female spline bottom parts (22c; 222c; 322c; 422c; 522c) formed on an inner peripheral part thereof, the female component configured to allow the male component to be slidably inserted thereinto in an axial direction thereby making up said shaft structure; and an elastic member (23; 223; 323; 423; 523; 823; 923; 1023; 1123; 1223; 1323) arranged on the male component such that a surface of the outer peripheral part of the male component is covered with the elastic member, wherein said shaft structure is configured such that in an initial state where the male component is inserted into the female component over a portion of the male component, the female and male components have a clearance (S1; S3; S4; S5; S6; S9; S10; S11; S12; S13; S14) generated between: sides of the plurality of female spline parts; and sides-facing portions of the elastic member such that with respect to at least part of said portion of the male component, the clearance gradually and continuously increases or decreases as a depth in an insertion direction increases, and when the male component is rotated with respect to the female component, a period of time, which elapses from the initial state to a state where the sides of the plurality of female spline parts and the portions of the elastic member abut on each other, has predetermined time differences along the axial direction. a male component (21; 221; 321; 421; 521; 821; 921; 1021; 1121; 1221; 1321) having a plurality of male spline parts (21c; 221c; 321c; 821c; 1221c; 1321c) and a plurality of male spline bottom parts (21d; 221d; 321d) formed on an outer peripheral part thereof; a female component (22; 222; 322; 422; 522; 822; 922; 1022; 1122; 1222; 1322) having a plurality of female spline parts (22b; 222b; 322b; 422b; 522b; 1122b) and a plurality of female spline bottom parts (22c; 222c; 322c; 422c; 522c) formed on an inner peripheral part thereof, the female component configured to allow the male component to be slidably inserted thereinto in an axial direction thereby making up said shaft structure; and an elastic member (23; 223; 323; 423; 523; 823; 923; 1023; 1123; 1223; 1323) arranged on the male component such that a surface of the outer peripheral part of the male component is covered with the elastic member, wherein said shaft structure is configured such that in an initial state where the male component is inserted into the female component over a portion of the male component, the female and male components have a clearance (S1; S3; S4; S5; S6; S9; S10; S11; S12; S13; S14) generated between: sides of the plurality of female spline parts; and sides-facing portions of the elastic member such that with respect to at least part of said portion of the male component, the clearance gradually and continuously increases or decreases as a depth in an insertion direction increases, and when the male component is rotated with respect to the female component, a period of time, which elapses from the initial state to a state where the sides of the plurality of female spline parts and the portions of the elastic member abut on each other, has predetermined time differences along the axial direction.