An air purifier according to the present invention includes: a tubular main body 2 having an inner space 3 surrounded by wall portions 6, 7, 8 having a plurality of air movement holes 12, 17; and a light applicator 4 in the inner space for throwing light toward inner surfaces of the wall portions. The inner side of the wall portions exposed to the light is made of a formed porous member. The formed porous member includes an inner surface having a surface part carrying a powdery photocatalyst capable of performing a photocatalytic reaction caused by light. The air purifier allows the carried photocatalyst to perform its catalytic action to a maximum, with a very simple construction.