To provide a torque sensor and an electric power steering device that can reduce the processing cost while improving the sensitivity of the torque sensor as well as securing the strength of a stopper.

In a torque sensor: coaxially disposed first and second rotational shafts 1, 2 are connected via a torsion bar 3; a cylindrical member 12 surrounding the outer circumferential surface of the first rotational shaft 1 is integrally formed in the rotational direction with the second rotational shaft; grooves 11b forming a plurality of projections 11a extending in the shaft direction as opposing the inner circumferential surface of the cylindrical member are formed on the first rotational shaft 1; windows 12a, 12b whose overlapping degree with the projections 11a changes are formed on the cylindrical member 12; and torque is detected based on the overlapping degree of the windows and the projections. Stopper grooves 11c regulating the relative rotation angle formed between the first and second rotational shafts are formed on the first rotational shaft 1 so that each set of a plurality of grooves 11b forming the projections 11a is grouped.