There is provided a high-sensitivity organic semiconductor radiation/light sensor and a radiation/light detector which can detect rays in real time. In the high-sensitivity organic semiconductor radiation/light sensor, a signal amplification wire 2 is embedded in an organic semiconductor 1. Carriers created by passage of radiation or light are avalanche-amplified by a high electric field generated near the signal amplification wire 2 by means of applying a high voltage to the signal amplification wire 2, thus dramatically improving detection efficiency of rays. Hence, even rays exhibiting low energy loss capability can be detected in real time with high sensitivity.