IEEE The 3-D magnetic recording using microwave-assisted magnetic recording has been proposed as one of the prospective recording technologies which uses a spin-torque oscillator (STO) as a reading sensor as well as a write-assisting device. In the reading process using an STO, the reproducing waveform is given as temporal dynamics of magnetization. We simulate the envelope of the waveform from recorded dots with the staggered magnetization configuration, which are calculated by using a micromagnetic simulation. We propose an envelope demodulation using two temporal magnetization dynamics from dual STO, and evaluate the bit error rate (BER) performance for partial response maximum likelihood system by the computer simulation. The result shows that our proposed system provides the signal-to-noise ratio improvement of 2.7 dB at the BER of 10⁻⁴.