A filling method for filling a container with animal litter, whereby large-sized granules and small-sized granules can be easily filled into containers in a predetermined blending ratio, and essentially the same blending ratio can be maintained for different containers. In a supply step in which the animal litter is supplied to a hopper, the animal litter is allowed to freely drop from above the storage space of the hopper, and in the storage space there are formed a first region in which the blending ratio of the small-sized granules with respect to the large-sized granules in a unit mass of the animal litter is equal to or less than the predetermined blending ratio and a second region in which the ratio is greater than the predetermined blending ratio, in an arrangement along the lengthwise direction of the storage space. Also, in a filling step in which the animal litter is filled into containers, delivery holes capable of delivering the animal litter of the first region and delivery holes capable of delivering the animal litter of the second region are selected, and the animal litter is delivered in the predetermined amount at least once each from each of the selected delivery holes, filling the containers so that the large-sized granules and small-sized granules in the unit amount are in the predetermined target blending ratio.