It sounds to me like a charango. Your song appears to be from Ecuador, where the charango is common.
The charango is a small Andean stringed instrument of the lute family, which probably originated in the Quechua and Aymara populations in the territory of the Altiplano in post-Colombian times, after European stringed instruments were introduced by the Spanish during colonialization. The instrument is widespread throughout the Andean regions of Bolivia, Peru, Ecuador, northern Chile and northwestern Argentina, where it is a popular musical instrument that exists in many variant forms.
About 66 cm (26 in) long, the charango was traditionally made with the shell from the back of an armadillo (called quirquincho or mulita in South American Spanish), but also it can be made of wood, which some believe to be a better resonator. Wood is more commonly used in modern instruments. Charangos for children may also be made from calabash. Many contemporary charangos are now made with different types of wood. It typically has ten strings in five courses of two strings each, but many other variations exist.
The charango was primarily played in traditional Andean music, but is more and more frequently being used by other Latin American musicians. A charango player is called a charanguista.
It's probably most familiar to the American audience as the guitar-like instrument used in the recording of "El Condor Pasa" that Simon & Garfunkel used as the instrumental track for their hit "If I Could." It's also used in Ariel Ramirez' "Gloria" from his Misa Criolla ("Creole Mass").