A torque measuring device for a rotating body is provided, which includes: a stationary section; a rotary section; a rotary transformer composed of a primary coil disposed at the stationary section, and a secondary coil disposed at the rotary section, wherein an electric power is transmitted from the stationary section to the rotary section by electromagnetic induction, a torque generated at a rotating body is detected at the rotary section by means of the electric power transmitted, and wherein a detection result is transmitted from the rotary section to the stationary section. In the torque measuring device, a capacitor is connected at the side of the secondary coil of the rotary transformer, and a series resonant circuit is formed by the capacitor in combination with a leakage inductance of the rotary transformer.