To prevent stratification in a low temperature liquefied gas tank without requiring a motive power.

A liquid rising pipe 17 on whose upper end a liquid flow out port 17b and on whose lower end a liquid suction port 17a are provided respectively is provided through a support member 18 so as to erect on the bottom surface in a low temperature liquefied gas tank 1. The liquid suction port 17a is opened in the low temperature liquefied gas 2 of the lower layer of the low temperature liquefied gas tank 1. The liquid flow out port 17b is projected on the liquid surface of the low temperature liquefied gas 2. A compressed BOG pipe 19 branched at the downstream position of a BOG compressor 6 is connected to the lower end of the liquid rising pipe 17 and the compressed BOG 4a is spouted from the lower end into the liquid rising pipe 17 and risen as a bubble 4b in the liquid rising pipe 17. The stirring of vertical direction is carried out by introducing and circulating the low temperature liquefied gas 2 from the downside to the uppertside in the liquid rising pipe 17 by the rise of the bubble 4b.