Provided are: a vein formation promoter containing phosphatidylcholine as an active ingredient and has an activity to promote the change of a tumor blood vessel to a vein； a blood vessel diameter dilator having an activity to dilate the diameter of a tumor blood vessel； a blood vessel connection promoter having an activity to connect tumor blood vessels to each other without involving a lysophospholipid receptor； a leukocyte infiltration promoter having an activity to promote the infiltration of a leukocyte into the whole area of a tumor without involving a lysophospholipid receptor； and a tumor immunity activator.
