Photodetection device and ranging device

A ranging device comprising:

• a laser light source that outputs coherent light;
• two or more photodetectors including respective light-receiving elements, the light-receiving elements being disposed separated from one another, the two or more photodetectors detecting, via the light-receiving elements, reflected light from a subject irradiated with the coherent light;
• a cross-correlation section that mixes two optical signals detected by any two photodetectors out of the two or more photodetectors;
• a heterodyne correlation section that mixes, with heterodyne mixing, the optical signals after mixing by the cross-correlation section or one of the optical signals before mixing by the cross-correlation section and a reference signal obtained by dividing the coherent light from the laser light source;
• and
• a signal processor that calculates distance information regarding the subject on a basis of a difference frequency component caused by a cross-correlation signal from the cross-correlation section and the reference signal.