The liquid injection device (10) comprises a microneedle (20) and a check valve (30). The microneedle (20) includes a base (21) having a first surface (21 S) and a second surface (21 T) which is a surface opposite to the first surface (21 S) (22) projecting from the first surface (21 S) toward the opposite side from the second surface (21 T) and a second surface (22) extending from the tip of the projection portion (22) along the extending direction of the projection portion And a through hole (24) penetrating through the through hole (21T), and the second surface (21T) forms a flow path through which the liquid agent (L) flows through the through hole (24). The check valve (30) is disposed in the flow path and suppresses the flow of the liquid agent (L) from the second surface (21T) toward the check valve (30).液剤注入装置(10)は、マイクロニードル(20)と逆止弁(30)とを備える。マイクロニードル(20)は、第1面(21S)と、第1面(21S)とは反対側の面である第2面(21T)とを有する基体(21)と、基体(21)の第1面(21S)から第2面(21T)とは反対側に向けて突き出た突起部(22)と、突起部(22)の延びる方向に沿って突起部(22)の先端から第2面(21T)までを貫通する貫通孔(24)と、を備え、第2面(21T)が貫通孔(24)に液剤(L)を流す流路を構成する。逆止弁(30)は、上記流路内に配置され、第2面(21T)から逆止弁(30)に向けて液剤(L)が流れることを抑える。
