The string instrument Väinämöinen plays in the Kalevala is the kantele.
The kantele is a traditional Finnish and Karelian plucked string instrument belonging to the Baltic zither family. It has a flat wooden body and strings stretched across it, so it is played by plucking rather than bowing. Older forms commonly had five or six horsehair strings, while later instruments used metal strings.
In the Kalevala, Väinämöinen first makes a magical kantele from the jawbone of a giant pike. Its music is extraordinarily beautiful: people, animals, and even supernatural beings gather to hear him play. The instrument therefore represents more than entertainment; it embodies the power of song, knowledge, and enchantment.
A fiddle is bowed, while a jouhikko is a bowed lyre, so neither is the instrument associated with Väinämöinen. Kanteletar is instead the title of a related collection of Finnish folk poetry published by Lönnrot.