Liquid agent injection device

A liquid agent injection device (10) comprising a microneedle (20) and a check valve (30). The microneedle (20) comprises: a base body (21) having a first surface (21S) and a second surface (21T) being a surface on the opposite side to the first surface (21S); protruding sections (22) protruding from the first surface (21S) of the base body (21) towards the opposite side to the second surface (21T); and through-holes (24) that penetrate from the tip of the protruding sections (22), along to the direction of extension of the protruding sections (22), to the second surface (21T). The second surface (21T) constitutes a flow path through which a liquid agent (L) flows to the through-holes (24). The check valve (30) is arranged inside the flow path and prevents the liquid agent (L) from flowing from the second surface (21T) towards the check valve (30).