PROBLEM TO BE SOLVED: To provide a method of keeping a liquid warm and preventing it from freezing, capable of keeping water in a water tank 40 warm and of preventing water in a toilet from freezing at a low cost.SOLUTION: A band-shaped heating element 30 is submerged in water W in a tank body 11. The band-shaped heating element 30 comprises a flexible printed wiring board 30b on which a plurality of LED chips 30a are mounted. Both of the front and the back of the flexible printed wiring board 30b as well as the LED chips 30a mounted on the board 30b are covered with a covering material 30e made from transparent soft thermoplastic polyvinyl chloride. The heat generated by the LED chips 30a keeps the water W warm, or prevents the water W from freezing.SELECTED DRAWING: Figure 1COPYRIGHT: (C)2018,JPO&INPIT【課題】低コストで水槽40の水の保温やトイレの水の凍結防止を可能にする液体の保温及び凍結防止方法を提供すること。【解決手段】タンク本体11内の水Wに帯状発熱体30を浸漬する。帯状発熱体30は複数個のLEDチップ30aを実装したフレキシブルプリント配線基板30bを備えている。フレキシブルプリント配線基板30bの表裏両面は、同基板30bに実装されたLEDチップ30aを含めて熱可塑性の透明な軟質ポリ塩化ビニルから成る被覆材30eで被覆されている。LEDチップ30aの発する熱で水Wを保温し、または水Wの凍結を防止する。【選択図】図1