An apparatus produces hydrate slurry, which is a mixture of aqueous solution and hydrate, by cooling aqueous solution containing a guest compound, which generates the hydrate at temperature higher than 0.degree. C., by using a cooling medium. The apparatus includes a first heat exchanger for supercooling the aqueous solution while holding the aqueous solution in a liquid state and in a second heat exchanger, which is provided on the downstream side of the first heat exchanger for cooling hydrate slurry.