Even if a cycle slip occurs in which reception of a positioning signal is interrupted, it is not necessary to estimate an integer bias again. A position during previous observation is updated on the basis of observation information from a sensor. The position during current observation is obtained by solving a modified observation equation obtained by applying a periodic function to an observation equation including a double difference of a carrier phase observed from a positioning signal from a satellite and eliminating the integer bias with the updated position as an initial value. For example, while an error in the position updated by the first calculation unit is less than ½ of a carrier wavelength, the second calculation unit solves the modified observation equation with the updated position as the initial value.