To provide a heat-resistant filter which is lightweight, has a low gas permeation resistance, a full life efficiency of 90%, and is excellent in processability and excellent in stability and fire resistance at high temperatures.

The filter is constituted from a nonwoven fabric prepared by binding a fibrous layer consisting of mixed fibers of heat-resistant staple fibers, high-tenacity fibers, and thermally bondable composite fibers with a flame-retardant resin binder, and has properties including lightness in a basis weight in the range of 70-200 g/m2, a bursting strength of 3.0 kPa, and an initial tensile modulus of 100 N/5 cm2/100% at 200C.