In order to produce a safe and sufficiently effective vaccine, the present invention addresses the issue of providing an adjuvant having a sufficiently strengthening action on immunity functions and having an extremely low likelihood of side-effects even when applied to a living body. An adjuvant including a phospholipid and a vaccine including said adjuvant and an antigen. In addition, a screening method for adjuvant candidate substances, that includes steps 1 and 2, namely: a step (1) in which an intracellular component and interferon regulatory factor 3 (IRF3) are caused to come in contact； and a step (2) in which the intracellular component which phosphorylates IRF3 is selected.
