Optical sensor and electronic device

An optical sensor comprising:

• a light-emitting unit that emits light in accordance with reference pulses;
• a first light-receiving unit that outputs pulses in response to light incident thereon;
• a first calculation unit that calculates, based on a number of first output pulses of the first light-receiving unit in response to light incident thereon including reflected light, which is emitted light of the light-emitting unit reflected from an object, and ambient light, a number of second output pulses of the first light-receiving unit in response to the ambient light incident thereon, and a ratio between a light-emission period and a non-light-emission period of the light-emitting unit, a number of third output pulses of the first light-receiving unit in response to the reflected light incident thereon;
• and
• a distance calculation unit that calculates a distance from this device to the object based on a result of comparison between the reference pulses and output pulses of the first light-receiving unit in the light-emission period if the number of third output pulses is greater than a first reference value.