According to one embodiment, a apparatus includes a coil, a clock generator, an echo transmitter, a carrier generator, a clock transmitter, a regenerator, an receiver, a reconstructor, a detector, and a controller. The echo transmitter generates and transmits an echo transmission signal synchronously with a clock signal generated by the clock generator to wirelessly transmit an echo signal output from the col. The carrier generator generates a carrier signal have a frequency within a variable range. The clock transmitter wirelessly transmits a clock transmission signal. The regenerator regenerates the clock signal based on the transmitted clock transmission signal. The receiver extracts the echo signal synchronously with the regenerated clock signal from the transmitted echo transmission signal. The detector detects a frequency of an interference wave. The controller controls the carrier generator to generate the carrier signal having a frequency which comparatively small interference with respect to the detected frequency.