A method for rapidly and highly sensitively measuring endotoxin is provided. Endotoxin is measured using an endotoxin-measuring agent comprising the proteins (1) to (3) below, each of which is a recombinant protein obtainable by being expressed using insect cells as a host: (1) a factor C derived from Tachypleus tridentatus, which factor C does not have a His-tag sequence at the C-terminus; (2) a factor B of a horseshoe crab; and (3) a proclotting enzyme of a horseshoe crab.
