To provide a slush LNG manufacturing method having high slush LNG manufacturing capacity and superior mixing performance of solid LNG and liquid LNG.

In this slush LNG manufacturing device wherein a liquid nitrogen tank is mounted in a liquefied natural gas tank, and a solid matter obtained by solidifying the liquefied natural gas is produced on a heat transfer face of a surface of the liquid nitrogen tank and scraped off by an auger to be mixed with the liquefied natural gas, the liquid nitrogen tank has the double cylindrical shape having a center axis vertically oriented, opened at its lower end, and having an inner peripheral face and an outer peripheral face of an inner circumferential wall part, and an inner peripheral face of an outer circumferential wall part as heat transfer faces, and comprises a first auger mounted on a rotating introduction shaft and rotated along the inner peripheral face of the inner circumferential wall part, an interlocking machine mounted on the rotating introduction shaft, a rotating shaft mounted on the interlocking machine in parallel with the rotating introduction shaft, and a second auger mounted on the rotating shaft, moved along the inner circumferential wall part and the outer circumferential wall part, and rotated between the inner circumferential wall part and the outer circumferential wall part.