To provide a building material exerting a VOC decomposing function, a deodorizing function and a dew condensation preventing function over a long period.

A building material treatment apparatus 100 includes two or more conveying rollers 107 serving as a means of moving a plate-like building material 101 in a specified direction, a first coating means 103 having e.g. a compressor 108a spraying a high-temperature far-IR-generating water HW1 containing a fixing agent on the building material 101 being conveyed, a second coating means 104 having e.g. a compressor 108b spraying a high-temperature far-IR-generating water HW2 containing powder RP of a far-IR-generating material on the building material 101 having been sprayed with the high-temperature far-IR-generating water HW1 containing the fixing agent and heating means 113a and 113b forming, respectively, the high-temperature far-IR-generating water HW1 containing the fixing agent and the high-temperature far-IR-generating water HW2 containing the powder RP of the far-IR-generating material.