Magnetic and optical properties an investigated for K clusters incorporated into zeolite LTA at loading densities of K atoms, n, between 1.0 and 3.2 per duster. No magnetic ordering is observed at n < 2. The spontaneous magnetization due to ferromagnetism is observed suddenly at n > 2. It is confirmed that the 1p-like quantum electronic stare of K cluster plays an essential role in the ferromagnetic phase.