  We present a simple approach to realize truly random number generation based
on measurement of the phase noise of a single mode vertical cavity surface
emitting laser (VCSEL). The true randomness of the quantum phase noise
originates from the spontaneous emission of photons and the random bit
generation rate is ultimately limited only by the laser linewidth. With the
final bit generation rate of 20 Mbit/s, the physically guaranteed truly random
bit sequence passes the three standard random tests. Moreover, for the first
time, a {\it continuously} generated random bit sequence up to 14 Gbit is
verified by two additional criteria for its true randomness.
