In a first pixel part, as an incident position is closer to a first end of a first pixel pair group in a second direction, an intensity of a first electric signal decreases. In a second pixel part, as the incident position is closer to the first end, an intensity of a second electric signal increases. In a third pixel part, as the incident position is closer to a second end of a second pixel pair group in a first direction, an intensity of a third electric signal decreases. In a fourth pixel part, as the incident position is closer to the second end, an intensity of a fourth electric signal increases. A calculation unit performs weighting on a first position on the basis of the third and fourth electric signals, and performs weighting on a second position on the basis of the first and second electric signals.