PROBLEM TO BE SOLVED: To provide a tea leaf comprising large amounts of umami ingredient irrespective of the season and place and without the influence of weather.SOLUTION: In at least a light volume suppression period (S6) after an embryo period (S4) for growth of a sprout of a tea tree (23), the tea tree (23) grown in the embryo period (S4) is irradiated with far-red light, as well as visible light in a wavelength range required for photosynthesis.【課題】季節及び場所を問わず、また天候の影響を受けることなく、旨味成分を多く含む茶葉を提供する。【解決手段】少なくとも茶樹(23)の新芽を生長させる萌芽期間(S4)後の光量抑制期間(S6)に、萌芽期間(S4)において生長した茶樹(23)に対して、光合成に必要な波長範囲の可視光とともに、遠赤色光を照射する。【選択図】図1