A rotating body load measuring device (100;200;300) for detecting a force acting on a rotating body that is formed in a columnar shape and rotates around its central axis, which is coaxial with a central axis of a shaft body protruding from a center of each of both end faces (31a,31b) of the rotating body, in a state where a main load is applied to the rotating body in a first direction (P,X) that is one direction in a radial direction, the rotating body load measuring device (100;200;300) comprising: a first support section which supports one end portion of the shaft body, which protrudes from one end face of the rotating body such that the one end portion of the shaft body is immovable in the first direction (P,X) and a second direction (Q,Y) along the central axis of the rotating body; a second support section which supports the other end portion of the shaft body, which protrudes from the other end face of the rotating body such that the other end portion of the shaft body is immovable in the first direction (P,X) and movable in the second direction (Q,Y); and a measuring part capable of measuring a force acting in the first direction (P,X) on at least one of the first support section and the second support section from the shaft body and capable of measuring a force acting in the second direction (Q,Y) on the first support section from the shaft body, characterized in that: the measuring part includes a first load cell capable of measuring forces acting in at least two directions of the first direction (P, X) and the second direction (Q, Y) and connected to the first support section and the one end portion of the shaft body so as to be immovable in the first direction (P, X) and the second direction (Q, Y), and a second load cell capable of measuring a force acting in at least one direction of the first direction (P,X) and connected to the other end portion of the shaft body, and the second support section includes a main body portion to which the second load cell is connected so as to be immovable in the first direction (P,X) and the second direction (Q,Y), a guide (56b;301) connected to one of the shaft body and the second load cell so as to be immovable in the first direction (P,X) and the second direction (Q,Y) and disposed along the second direction (Q,Y), and a slider (56c;302) connected to the other of the shaft body and the second load cell so as to be immovable in the first direction (P,X) and supported on the guide (56b;301) so as to be movable in the second direction (Q,Y). a first support section which supports one end portion of the shaft body, which protrudes from one end face of the rotating body such that the one end portion of the shaft body is immovable in the first direction (P,X) and a second direction (Q,Y) along the central axis of the rotating body; a second support section which supports the other end portion of the shaft body, which protrudes from the other end face of the rotating body such that the other end portion of the shaft body is immovable in the first direction (P,X) and movable in the second direction (Q,Y); and a measuring part capable of measuring a force acting in the first direction (P,X) on at least one of the first support section and the second support section from the shaft body and capable of measuring a force acting in the second direction (Q,Y) on the first support section from the shaft body, characterized in that: the measuring part includes a first load cell capable of measuring forces acting in at least two directions of the first direction (P, X) and the second direction (Q, Y) and connected to the first support section and the one end portion of the shaft body so as to be immovable in the first direction (P, X) and the second direction (Q, Y), and a second load cell capable of measuring a force acting in at least one direction of the first direction (P,X) and connected to the other end portion of the shaft body, and the second support section includes a main body portion to which the second load cell is connected so as to be immovable in the first direction (P,X) and the second direction (Q,Y), a guide (56b;301) connected to one of the shaft body and the second load cell so as to be immovable in the first direction (P,X) and the second direction (Q,Y) and disposed along the second direction (Q,Y), and a slider (56c;302) connected to the other of the shaft body and the second load cell so as to be immovable in the first direction (P,X) and supported on the guide (56b;301) so as to be movable in the second direction (Q,Y).