The force acting on the electric charge of electron gives rise to the electro-motive force. This is Faraday’s law in the classical electromagnetism discovered in 1831. It is noted that the modern electric industry started with this law. Here we show that the force acting on the electron spin gives rise to a motive force, i.e., "spin-motive force". This generalized Faraday’s law reflects the conservation of the magnetic energy of a ferromagnet with the electrical energy of the conduction electrons via the mutual exchange interaction. We discuss that the spin-motive force may play a key role in spin-electronics, i.e., spintronics.