Excitation-use high frequency RF generated by an RF oscillator is modulated by a modulator based on control by a pulse control unit, to give a pulse form. The generated RF pulse is then amplified by an RF amplifier, and set to a small-sized RF coil. The small-sized RF coil applies the RF pulse to a specific position of a sample placed on a sample stage, and detects echo signals of the RF pulse. The echo signal is amplified by a preamplifier, and is then sent to a phase detector. The phase detector detects the echo signal, and sent it via an A/D converter to an operation unit. The operation unit calculates T2 relaxation time constant based on intensity of the echo signal, and the water content at the predetermined position of the sample is calculated based on the calculated T2 relaxation time constant.