[Problem] To provide an agent for hypodermic injection that has excellent flow characteristics, can, in particular, be used even in thin needles such as needles having an internal diameter of no more than 0.20 mm, and is unlikely to cause pain during injections or inflammation. [Solution] An agent for hypodermic injection, characterized by: having hydrogel containing sintered hydroxyapatite particles； the sintered hydroxyapatite particle content being 1%-60% by mass, relative to the total mass of the agent； and the average diameter of the sintered hydroxyapatite particles being no more than 15 µm.
