A rotating body load measuring device (100) according to the present invention detects a force acting on a rotating body (30) that is formed in a columnar shape and rotates around a central axis (L60) of a shaft body (60) protruding from a center of an end face, in a state where a main load is applied to the rotating body (30) in a main load direction (P) that is one direction in a radial direction, and includes a load cell (70) having a measurement center (C70) and capable of measuring forces acting in at least three directions with the measurement center (C70) as a reference, in which the load cell (70) is disposed such that the measurement center (C70) and the central axis (L60) overlap when viewed in the main load direction (P), and is connected to the shaft body (60).