A layout design device that designs a new layout obtained by changing an existing layout related to arrangement of a facility in a certain space, the layout design device including: a generator that generates a new layout according to stay data related to a stay specified from flow line data representing a motion of a target in a case of a existing layout in a space; and an output processor that outputs the new layout generated by the generator, wherein the generator generates the stay data by extracting a stay portion where the target stays from the flow line data, and generates the new layout by using auxiliary information that associates the facility arranged in the space with the stay portion and the stay data.