Image sensor and image-capturing apparatus

An image sensor includes: a first light-receiving unit that: receives a modulated optical signal having being reflected on an image-capturing target and including a modulated component with an intensity modulated at a predetermined modulation frequency; and outputs a first electrical signal; a second light-receiving unit that: receives a reference optical signal with an intensity modulated in synchronization with the modulated optical signal; and outputs a second electrical signal; and a detecting unit that: is provided to a substrate stacked on a substrate including the first light-receiving unit; refers to the second electrical signal; and detects, from the first electrical signal, a third electrical signal corresponding to the modulated component.