The present invention provides a new insect pest control agent that can instantly stop the movement of an insect pest and kill the insect pest, but that does not have a risk of explosion or ignition and that does not destroy the ozone layer and that has a low global warming potential, and therefore that can be safely used.An insect pest control agent comprising 1-chloro-3,3,3-trifluoropropene as an active agent solves the above problem.本發明提供一種新穎害蟲防除劑,其可瞬時定住害蟲之活動,進行殺蟲,而且亦無爆炸或引火之虞及臭氧層之破壞,全球暖化係數較低,可安全地使用。本發明製成以1-氯-3,3,3-三氟丙烯為有效成分之害蟲防除劑。