  We present the environmental dependence of colour, stellar mass, and star
formation (SF) activity in H-alpha-selected galaxies along the large-scale
structure at z=0.4 hosting twin clusters in DEEP2-3 field, discovered by Subaru
Strategic Programme of Hyper Suprime-Cam (HSC SSP). By combining photo-z
selected galaxies and H-alpha emitters selected with broad-band and narrow-band
(NB) data of the recent data release of HSC SSP (DR1), we confirm that galaxies
in higher-density environments or galaxies in the cluster central regions show
redder colours. We find that there still remains a possible colour-density and
colour-radius correlation even if we restrict the sample to H-alpha-selected
galaxies, likely due to the presence of massive H-alpha emitters in denser
regions. We also find a hint of increased star formation rates (SFR) amongst
H-alpha emitters towards the highest-density environment, again primarily
driven by the excess of red/massive H-alpha emitters in high-density
environment, while their specific SFR does not significantly change with
environment. This work demonstrates the power of the HSC SSP NB data to study
SF galaxies across environment in the distant universe.
