  The neutron lifetime has been measured by comparing the decay rate with the
reaction rate of $^3$He nuclei of a pulsed neutron beam from the spallation
neutron source at the Japan Proton Accelerator Research Complex (J-PARC). The
decay rate and the reaction rate were determined by simultaneously detecting
electrons from the neutron decay and protons from the $^3$He(n,p)$^3$H reaction
using a gas chamber of which working gas contains diluted $^3$He. The measured
neutron lifetime was $898\,\pm\,10\,_{\rm stat}\,^{+15}_{-18}\,_{\rm sys}\,$s.
