magnetic sections 46 is p in this case the magnetic section 45 and non magnetic sections 46 may be of an equal length of p 2 or may be of different lengths according to this embodiment the coil assembly 41 is constructed so as to work at four phases which are for the sake of convenience denoted in the drawings by reference characters a c b and d positional relationship between the sensor rod 23 and coil assembly 41 is such that reluctances produced in the four phases a c b d in correspondence with the position of the sensor rod 23 are different or shifted by 90 u00b0 from one another in correspondence with the position of the sensor rod 23 for example when the phase a is a cosine phase the phase c will be a minus cosine phase the phase b will be a sine phase and the phase d will be a minus sine phase in the example shown in fig4 pairs of the primary coils 1a 1b 1c 1d and secondary coils 2a 2c 2b 2d are provided respectively for the phases a c b d the secondary coils 2a 2c 2b 2d are wound outwardly of the corresponding primary coils 1a 1b 1c 1d in the illustrated example each of the primary coils 1a 1b 1c 1d and secondary coils.