A kit and a method are provided for easily measuring the concentration of an active ingredient of a termite insecticide persisting in soil, particularly on site where a termite insecticide was actually applied. A kit of the present invention comprises 1) an extraction unit for extracting, with an solvent, a termite insecticide active ingredient from an object of measurement and 2) a reaction unit including a reaction container for encapsulating an identifying antigen, a fixing member for immobilizing an antibody against an active ingredient, and a sealing member capable of fitting to the reaction container. The kit optionally includes 3) a detection unit for visually or optically detecting a change depending on the concentrations of the active ingredient in the object of measurement, and 4) a dilution unit for diluting the sample solution to a certain ratio.