A stowage pattern calculation device calculates positions of articles irregularly conveyed. The plurality of articles have a box shape and include articles having dimensions different from each other. The stowage pattern calculation device includes a combination calculation part which calculates a combination of the articles constituting a layer formed in a storage area and selects a layer of the articles based on types of the articles, a height of the layer, and an area of the layer. The stowage pattern calculation device includes a position determination part which calculates a first probability of completion of the layer and determines positions at which the articles are stacked based on a positional relationship between a robot and the storage area and the first probability.