PURPOSE: To facilitate adjustment and correctly achieve the resonance condition by providing an adjusting mechanism for the between electrode plate distance of each condenser and permitting the between electrode plate distance of each condenser to vary by equal quantity and keeping the static electric capacity of each condenser at equal value.

CONSTITUTION: An RF coil 1a is formed on a cylindrical body 3, and a small cylindrical body 5 is installed on the cylindrical body 3. One electrode plate 11b of a condenser is fixed onto the small cylindrical body 5, together with an inductance L2, and the distance between the electrode plates 11a and 11b for each condenser is continuously varied and adjusted by shifting the cylindrical body 5 in parallel on the cylindrical body 3. In other words, the small cylindrical body 5, groove 9, and a projecting part which is formed on the small cylindrical body 5 so as to be fitted into the groove 9 constitute a between-condenser electrode plate distance adjusting mechanism. Further, since, one electrode plate 11b of each condenser is fixed onto the small cylindrical body 5, the shift of the electrode plate is interlocked, and the shift by an equal quantity is carried out, and the static electric capacity of each condenser varies by an equal quantity during the adjusting process, and the correct adjustment is permitted.