An apparatus for preparing foam from a milk-based liquid. The apparatus (1) includes: a support base; a container containing an amount liquid, the container being arrangeable in a working position on the support base; a stirrer adapted to be removably positioned in the container to rotate about an axis of rotation; and a driving device, positioned outside the container (3) and arranged to be magnetically coupled with the stirrer to drive it in rotation about the axis of rotation to stir the liquid contained in the container and form the foam. The driving device includes a stator (12) disposed around a member of the stirrer (8) generating a rotating magnetic field about the axis of rotation for inducing a rotation of the member (9) to drive the stirring device.