Observations of high-z galaxies have successfully obtained a glimpse of what 
happened in the early stage of the universe. In this contribution, we describe 
two topics which closely relate with each other: 
(1) We summarize observational findings obtained so far on high-redshift 
star-forming galaxies. We especially put emphasis on our studies of Lyman 
break galaxies at z~5 based on wide-field Suprime-Cam imaging and follow-up 
observations with Subaru/FOCAS, Gemini/GMOS and Spitzer/IRAC. With UV 
luminosity function, spectroscopic features and stellar population estimates 
through SED fitting, we attempt to draw a picture of galaxy evolution in the 
early epoch of the universe, by the comparison of such properties at different 
redsfhits.
(2) Star-forming galaxies are also strong candidates of the source of ionizing 
radiation in the epoch of the cosmic reionization. Although observational 
constraints on its process have been gradually accumulated, the escape fraction 
(or emissivity) of ionizing radiation has been poorly constrained. Here we 
briefly describe our recent discoveries of strong emitters of ionizing radiation 
at z~3. Counterparts of such strong ionizing radiation emitters at the epoch 
of reionization could be a primary source of ionizing radiation.
We also would like to make some notes what are required in the coming decade 
to step further toward the real understanding of the galaxy formation and the 
cosmic reionization.