Properties of galaxies are strong functions of environment. However, the origin of such environmental dependence of galaxies is still unclear and is one of the biggest issues in the extra-galactic astronomy. In my talk, I will present our recent H-alpha emitter survey for two distant galaxy clusters at z=0.4 and z=0.8, with narrow-band filters of Suprime-Cam and MOIRCS on the Subaru Telescope. Taking advantage of the wide-field capability of these facilities, we investigate in detail the star forming activity in and around the clusters. In particular, we report a discovery of a large number of red star forming galaxies (probably the transition galaxies) and/or MIR-detected dusty starbursts (revealed by our wide-field MIR imaging with AKARI satellite), especially in galaxy groups and in the filamentary structures relatively far away from the cluster. Our results suggest that properties of galaxies are indeed changing 'before' entering cluster environment and that group-scale environment at z<1 may have played an important role in the evolution of the present-day cluster galaxies. We have recently launched "MAHALO-Subaru" project, which is a direct extension of our study toward the more distant Universe (z>>1). I will briefly introduce the concept and very recent progress of this project as well.