To safely carry out the extermination and prevention of infestation of insect pests such as a rice weevil in a rice chest by housing a liquid impregnated material impregnated with a perillaldehyde-based chemical in an air- permeable case.

This thermal volatilizer is obtained by adding preferably a volatilization inhibitor or an antioxidant to a chemical consisting essentially of perillaldehyde, impregnating a member 1 with the resultant mixture, housing the liquid impregnated member 1 in a wrapping material 2 for easing the volatilization and housing the resultant wrapping material 2 in an air-permeable case 3 made of a synthetic resin. The liquid impregnated member 1 is preferably fixed in a nipping part provided in the openable and closable air-permeable case 3.