Abstract: A high-frequency amplifier apparatus according to an embodiment amplifies high-frequency signals; and includes a balun, amplification circuitry, and matching circuitry. The balun transforms unbalanced signals, which are input, into balanced signals. The amplification circuitry amplifies the balanced signals output from the balun. The matching circuitry is disposed in between the balun and the amplification circuitry, and performs impedance matching. The balun includes an auxiliary winding that is connected to a port of the balun.

Abstract: In one embodiment, an MRI apparatus includes: an RF coil configured to apply a radio frequency (RF) signal of a Larmor frequency of a spin species in an object; and an amplifying apparatus configured to amplify the RF signal and supply the amplified RF signal to an output that is connectable to a load (80) that includes at least the RF coil and the object, wherein: the amplifying apparatus includes two amplification circuits provided in parallel and an impedance transformation circuit; and the impedance transformation circuit is provided between the load and an output terminal of one of the two amplification circuits such that a polarity of reactance as viewed from an output terminal of one of the two amplification circuits toward the load is opposite to a polarity of reactance as viewed from an output terminal of another of the two amplification circuits toward the load.