Torque sensor

A torque sensor comprising:

• a first structure including a first surface in an annular shape, a second surface in the annular shape and parallel to the first surface, a third surface connecting the first surface with an outer circumference of the second surface, and a fourth surface connecting the first surface with an inner circumference of the second surface;
• a second structure in the annular shape and concentrically arranged inside the first structure;
• a plurality of third structures connecting the first structure with the second structure;
• and
• a plurality of strain sensors coupled between the first structure and the second structure, and
• the first structure comprising a plurality of protrusions on a part of the third surface, the plurality of protrusions including an inclined part becoming higher in a direction from the first surface to the second surface and a contact part continuous from a vertex of the inclined part, parallel to the third surface, and in a liner shape.