A filament lamp comprising a bulb which has a hermetically sealed portion on at least one end and multiple filament assemblies, each filament assembly comprising a coiled filament and connected leads to supply power to that filament, the filament assemblies being sequentially arranged in the axial direction of the bulb, the leads of each filament assembly being electrically connected to respective multiple conductive parts set in the sealed portions, and power being independently suppliable to each of the filaments. A respective one of the coiled filaments is located in a respective first quadrant formed by intersecting planes that are perpendicular to each other and that are tangent to an outer coil diameter of the respective coiled filament. The leads are positioned in quadrants other than the quadrant in which the coiled filament is located. A light irradiation type heat treatment apparatus uses a plurality of such filament lamps.