PURPOSE:To provide the above activation agent composed of a water extract or ethanol extract liquid of tea leaves, effective in promoting the proliferation of bifidus bacteria, enabling sufficient growth even in intestines and improving the production efficiency of bifidus bacteria. CONSTITUTION:The objective activation agent is composed of water-extract (preferably extract of hot water of >=60 deg.C) or ethanol extract of tea leaves. The tea is preferably green tea, oolong tea, black tea or pooal tea.