A torque sensor 1 is provided with two shafts 3, 4 (input shaft 3 and output shaft 4) which constitute a shaft member 2, which is a torque detection object, an elastic member 5 which connects the shafts 3 and 4 coaxially, and a torsion angle of the elastic member 5 is detected as a torque which affects on the shaft member 2. The torque sensor 1 is provided with a hard magnetic member 6 which generates a magnetic flux therearound, a pair of first soft magnetic members 7, 8 which constitute a first magnetic circuit H1 together with the hard magnetic member 6 to change a reluctance by torsion of the elastic member 5, a pair of second soft magnetic members 9, 10 which constitute a second magnetic circuit H2 together with the hard magnetic member 6 to keep the reluctance constant, and a flux detection means 12 which detects a flux density of the second magnetic circuit H2 that varies in accordance with a torsion angle of the elastic member 5.