A reference core position calculation device 100 that calculates a reference core position of an elevator shaft in which an elevator is to be installed includes a measurement unit 101 and a calculation unit 112. The measurement unit 101 measures a dimension of each portion of the elevator shaft. The calculation unit 112 calculates portion dimension values of the elevator shaft based on the reference core position and the dimension of each portion measured by the measurement unit 101. When the reference core position is a first reference core position, the calculation unit 112 determines whether portion dimension values of the elevator shaft calculated based on the first reference core position satisfy a predetermined specification.