PURPOSE: To improve a repellent effect to the harmful insect to be generated through living environment such as a flea, tick and cockroach by improving safety and keeping the repellent effect for a long period of time, by a method wherein a repellent is volatilized and scattered into the air gradually by impregnating the inside uniformly with the specific repellent for the harmful insect.

CONSTITUTION: A toluamide repellent for a harmful insect constituted of a formula shown is used as a repellent for the harmful insect. Then the repellent for the harmful insect is infiltrated into a ligneous fiber obtainable by fibrillating a wood chip. The obtainable treated chip is made a fiber mat by forming the same after application of an adhesive agent and the fiber mat is clamped down and stuck. When the fiber sheet formed in this manner is used as a base material for a ceiling or a ceiling material by decorating the same, the harmful insect to be generated through living environment can be prevented effectively from invading into the ceiling from the outside or into a room from the inside or the ceiling. Also of development/breeding of the harmful insect to be generated through the living environment in the ceiling can be prevented further. In the formula, R1 and R2 are H, CH3, C2H5, C3H7, C4H9, C5H11, C6H13, C7H15, C8H17, C9H19 and C10H21.