The present invention relates to a fishing sinker having a weight adjustment device using volume change. According to the present invention, the fishing sinker is composed of an upper cap and a lower cap that are screwed to each other such that an internal void is expanded or shrunk by fastening or loosening screw in a sealed state, and is hung to an end of a fishing gut to allow a fishing hook to sink under the water. The volume of the fishing sinker changes according to the degree of a screw fastening, so the pressure acting on the fishing sinker is increased/decreased in proportion to the amount of a volume increase/decrease of the sinker when the sinker is sunk under the water, and thus the weight of the sinker can be easily adjusted to correspond to the buoyancy of a float. According to the present invention, the sinker is composed of the upper and lower caps that are screwed to each other, wherein the upper cap comprises: a cylindrical sleeve provided on outer portion thereof to guide insertion of screw for screwing and a screw rod formed to be located on a concentric line therein while maintaining a gap from the inner circumferential surface of the sleeve, and the lower cap comprises: a screw groove screwed to the screw rod in correspondence thereto and a screw tube having one or more rings provided on an upper outer circumferential surface thereof to serve a sealing function. Thus the lower cap is inserted or separated through the gap between the sleeves, and the volume is changed while the internal space of the screw groove is reduced or expanded in the sealed state according to the degree of the screwing between the upper and lower caps, so the weight of the sinker under the water is added or reduced in proportion to the amount of the volume change thereof.본 발명은 낚싯바늘을 물속에 가라앉도록 낚싯줄의 끝에 매달게 되는 봉돌을 나사 조임이나 풀림에 의해 실링(sealing) 상태에서 내부공간이 축소 또는 확대되도록 상호 나사결합되는 상부캡과 하부캡으로 구성하여 그 나사결합 정도에 따라 체적을 변화되게 함으로써, 상기 봉돌을 수중에 침수되게 하였을 때 봉돌의 체적변화량에 비례하는 만큼 봉돌에 가해지는 압력차에 의해
