Disclosed are a measurement method and a measurement reagent, both of which are specific to insulin and enable the accurate measurement of only insulin with high sensitivity without the influence from proinsulin or any insulin-like compound. Specifically disclosed are a measurement method and a reagent, both of which enable the specific measurement of insulin by utilizing an antibody incapable of reacting with insulin that is not bound to an anti-insulin antibody but capable of reacting with insulin that is bound to an anti-insulin antibody.