PURPOSE: To detect the blade pitch angle of an engine propulsor by measuring the time between signal pulses generated by a magnetic field-signal exchanger arranged to an engine part adjacent to the propulsor.

CONSTITUTION: The time between pulses is found out by a relative position of a pitch wheel 24 and a fixed wheel 27 acting as a magnetic field variable inducer on a propulsor 14. A magnetic field-signal converter such as a coil 28 is arranged sufficiently approaching to a fixed tab 26 and pitch tab 25. As a result, the magnetic field generating a magnetic field property 28a staying on the center of the coil 28 is fluctuated by the tabs 25, 26. An alternating voltage is generated in the coil 28 by this magnetic field fluctuation and the pitch of the blade 12 is decided by the pulse of this alternating voltage. The pitch of the blade 16 on an outhub 18 is detected alike. Therefore, it is unnecessary to install a breakable electric machine device in the propulsor and the measurement device with a high reliability is made.