The invention provides a true random number generator, which comprises a light transmitting secondary module, at least one light receiving secondary module, a clock source, an attenuator and a sampling device, wherein the clock source sends clock signals to the light transmitting secondary module and the sampling device; the light transmitting secondary module transmits light signals according tothe clock signals; the light receiving secondary module receives the light signals, and the light power received by the light receiving secondary module is less than or equal to the detection sensitivity of the light receiving secondary module; the sampling device samples output signals of the light receiving secondary module according to the clock signals of the clock source and a predetermined threshold value. The quality of random numbers generated by the true random number generator is not influenced by environment; the true random number generator has the advantages of strong anti-jamming capacity, high generation rate and low cost, and also can adopt a plurality of light receiving secondary modules to work in parallel so as to acquire doubled random number output; and the true random number generator also can adopt a TTL standard level as an authentication amplitude so as to leave out sampling and comparing circuits for noise signals and greatly simplify the circuit structure.