To reduce manufacturing costs in arranging a transmission part inside a torque transmission shaft via an attachment part, by simplifying the processing for forming a hollow space and the attachment part inside the shaft.

A torque sensor comprises: a torque transmission shaft 2, which is shaped in a hollow shaft and made of a steel material, for transmitting a torque with torsion between a driving side X1 and a loading side X2; a distortion detection part for detecting distortion arising on an inner peripheral surface 2a of the torque transmission shaft due to a torque input; and a transmission part 30 for transmitting a detection result of the distortion detection part to the outside of the torque transmission shaft 2. An engagement shaft 8 is provided that is shaped in a hollow shaft, and that engages with the torque transmission shaft at the inner peripheral side thereof to form a double hollow shaft together with the torque transmission shaft, while a hollow space SP0 of the engagement shaft is formed with electrical connection between a first hole 8h₁, which passes through a shaft center Cn and is directed from an end part 8d of the loading side towards an end part 8c of the driving side, and a second hole 8h₂, which is formed between outer peripheral surfaces 8b and 8b in a radial direction X3. An attachment part 80, which is a slit for holding the transmission part, is formed on an inner surface of the engagement shaft.