An insect pest control method of using an insect pest control product comprising a thermal vaporization/diffusion absorbent wick for vaporizing and diffusing a water-based insecticidal composition, the method comprising: putting the thermal vaporization/diffusion absorbent wick in the water-based insecticidal composition so that the water-based insecticidal composition is absorbed and transported to a top portion of the thermal vaporization/diffusion absorbent wick, and heating the top portion of the thermal vaporization/diffusion absorbent wick at 80 to 150°C so that a pyrethroid insecticidal component is vaporized and diffused into the atmosphere, wherein the thermal vaporization/diffusion absorbent wick is a baked wick, wherein the water-based insecticidal composition contains 0.1 to 3.0 mass% of the pyrethroid insecticidal component which is transfluthrin, 30 to 60 mass% of a glycol ether compound which is diethylene glycol monoalkyl ether and/or a glycol compound, said compounds having a boiling point of 150 to 300°C, and water, wherein the product further comprises a hollow tube-shaped heat generator for heating the thermal vaporization/diffusion absorbent wick with the heat generator surrounding the absorbent wick, wherein a surface temperature of the hollow tube-shaped heat generator is set to 80 to 150°C, wherein an average gap distance between an outer surface of the thermal vaporization/diffusion absorbent wick and an inner surface of the hollow tube-shaped heat generator is set to 1.2 to 1.8 mm, wherein an inner diameter of an inner wall of the hollow tube-shaped heat generator is 10 mm and a height (b) of the hollow tube-shaped heat generator is set to 8 to 12 mm, and wherein a ratio (a)/(b) of a length (a) of the top portion of the thermal vaporization/diffusion absorbent wick facing the inner wall of the hollow tube-shaped heat generator to the height (b) of an inner wall of the hollow tube-shaped heat generator is 0.7 to 0.8 while a concentration of the pyrethroid insecticidal component in diffused vapor particles one hour after the start of vaporization and diffusion is 1.5 to 18 times as high as a concentration of the pyrethroid insecticidal component in diffused vapor particles of initial vaporization and diffusion. putting the thermal vaporization/diffusion absorbent wick in the water-based insecticidal composition so that the water-based insecticidal composition is absorbed and transported to a top portion of the thermal vaporization/diffusion absorbent wick, and heating the top portion of the thermal vaporization/diffusion absorbent wick at 80 to 150°C so that a pyrethroid insecticidal component is vaporized and diffused into the atmosphere, wherein the thermal vaporization/diffusion absorbent wick is a baked wick, wherein the water-based insecticidal composition contains 0.1 to 3.0 mass% of the pyrethroid insecticidal component which is transfluthrin, 30 to 60 mass% of a glycol ether compound which is diethylene glycol monoalkyl ether and/or a glycol compound, said compounds having a boiling point of 150 to 300°C, and water, wherein the product further comprises a hollow tube-shaped heat generator for heating the thermal vaporization/diffusion absorbent wick with the heat generator surrounding the absorbent wick, wherein a surface temperature of the hollow tube-shaped heat generator is set to 80 to 150°C, wherein an average gap distance between an outer surface of the thermal vaporization/diffusion absorbent wick and an inner surface of the hollow tube-shaped heat generator is set to 1.2 to 1.8 mm, wherein an inner diameter of an inner wall of the hollow tube-shaped heat generator is 10 mm and a height (b) of the hollow tube-shaped heat generator is set to 8 to 12 mm, and wherein a ratio (a)/(b) of a length (a) of the top portion of the thermal vaporization/diffusion absorbent wick facing the inner wall of the hollow tube-shaped heat generator to the height (b) of an inner wall of the hollow tube-shaped heat generator is 0.7 to 0.8 while a concentration of the pyrethroid insecticidal component in diffused vapor particles one hour after the start of vaporization and diffusion is 1.5 to 18 times as high as a concentration of the pyrethroid insecticidal component in diffused vapor particles of initial vaporization and diffusion.