  We investigate the possibility to have a constraint on the mass of thermal
warm dark matter (WDM) particle from the expected data of the Wide Field
Infrared Survey Telescope (WFIRST) survey if all the dark matter is warm. For
this purpose we consider the lensing effect of large scale structure based on
the warm dark matter scenario on the apparent magnitude of SNe Ia. We use
HALOFIT as non-linear matter power spectrum and the variance of PDF. We preform
a Fisher matrix analysis and obtain the lower bound of $m_{\rm WDM}>0.167$keV.
