Excitation-use high frequency RF generated by an RF oscillator 102 is modulated by a modulator 104 based on control by a pulse control unit 108, to give a pulse form. The generated RF pulse is then amplified by an RF amplifier 106, and set to a small-sized RF coil 114. The small-sized RF coil 114 applies the RF pulse to a specific position of a sample placed on a sample stage 116, and detects echo signals of the RF pulse. The echo signal is amplified by a preamplifier 112, and is then sent to a phase detector 110. The phase detector 110 detects the echo signal, and sent it via an A/D converter 118 to an operation unit 130. The operation unit 130 calculates T.sub.2 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 T.sub.2 relaxation time constant.