  The properties of the spin-down age are investigated. Based on assumption
about a uniform magnetic field decay law we suggest a new method which allows
us to shed light on magnetic field decay. This method is applied for following
selection: isolated non-millisecond pulsars from the ATNF catalog are chosen.
Pulsars in the selection are with the spin-down ages from 4 \cdot 10^4 to 2
\cdot 10^6 years. In order to avoid observational selection we take into
account only pulsars which are closer to the Sun than 10 kpc. For this
selection we restore the uniform magnetic field decay law. It appears that the
magnetic field decays three times from 4 \cdot 10^4 to 3.5 \cdot 10^5 years.
This function is approximated by modified power-law. We also estimate the
birthrate of pulsars in our Galaxy and find that it should be about 2.9 pulsars
per century.
