It is known that the galaxy properties are strongly affected by surrounding environments during the course of accretion to rich cluster cores. Such environmental effects are also clearly seen in a z~1 cluster we observed with SWIMS on Subaru. SWIMS is a new instrument for the University of Tokyo Atacama Observatory (TAO) but is now brought on Subaru Telescope. Although the observation was a part of the engineering runs to test the first deep imaging observations with SWIMS, we fortunately get some interesting results based on a narrow-band H-alpha imaging data, combined with Subaru HSC optical imaging data as well as a rich suit of existing data (HST, Spitzer and intensive spectroscopic survey). We will discuss how the mergers and starburst are activated and then quenched as galaxy groups fall into the cluster core.