Large scale structure in the universe adds inevitable noise to any cosmological observation by its weak lensing effect. However it also carries important cosmological information if we can predict the details of the effect. In this talk l consider the effect on the magnitude-redshift relation of type Ia supernovae as an example. I show that the observation of the effect can be used to constrain the total neutrino mass of the order of 0.5 eV which is comparable to CMB alone and dark energy properties by future imaging surveys with the Wide-field Infrared Survey Telescope and Large Synoptic Survey Telescope. Also, possible improvements of the constraints are discussed.