In this paper, we introduce an energy-efficient true random number generator (TRNG) using triple read-write data-stream multiplexing combined CMOS-circuits with three-terminal magnetic tunnel junction (3T-MTJ) devices. When multiple 3T-MTJ devices are used and sequentially activated for high-speed random-number generation, the sufficient timing margin must be guaranteed for correct random-number bit stream from the 3T-MTJ devices. In the proposed TRNG, random-number bit streams are triplicated and three individual random-number bit streams are superposed among them on a single output line, which achieves high-speed and energy-efficient random number generation. We use 65 nm-CMOS/3T-MTJ design technologies, and confirm its correct operation verification by HSPICE simulation with a 3T-MTJ model. The quality of random numbers generated is verified by NIST test. As a result, the energy consumption per bit is 0.5 pJ / bit, which is about 1/10 of a conventional CMOS-based TRNG.