To provide a thermal volatilizing system applicable to a conventional electric mosquito-repellent tool equipped with a heat radiating plate having the nearly same area as that of a mat, usable together with a conventional mat for one day and capable of sustaining stable insecticidal efficacies over a long time of ≥5 days.

This insecticidal mat for a long time is equipped with a clip provided with a pedestal having 2.0-4.0 mm height and nipped along one lateral end in the transverse direction of the base of the mat made of a pulp and having 20-24 mm length, 32-38 mm breadth and 2.0-3.0 mm thickness. The mat comprises ≥50 mg of a pyrethroid insecticidal ingredient having ≥4.0×10-6 mmHg vapor pressure at 20°C and a volatilization regulator in a weight ratio of ≥0.3 based on the pyrethroid insecticidal ingredient.