In recent years, variable sky has been intensively studied by wide-field survey observations. Such transient surveys have discovered many supernovae and also previously unknown transient events. After briefly introducing transient surveys in these years, I will introduce our activity for two optical transient surveys in Japan. One is Kiso Supernova Survey (KISS) using a 4 deg^2 wide-field camera of the 1.05m Kiso Schimidt telescope, This survey focuses on short-timescale phenomena, such as shock breakout of supernovae. The other is a planned transient survey using Hyper Suprime Cam (HSC) of the 8.2m Subaru telescope.