There is provided a high-frequency amplifier including a divider, a plurality of amplifiers for amplifying a high-frequency signal distributed by the divider and outputting the amplified high-frequency signal, a combiner for combining amplified high-frequency signals, a base substrate, a conductor pattern that is connected to a ground end of each of the amplifiers, and a ground electrode. Each of the conductor patterns has a first conductive portion. A slot is disposed between the two conductor patterns connected to the corresponding adjacent amplifiers. Between the adjacent amplifiers, two vias are formed so that the slot is sandwiched between the vias. One of the two conductor patterns is connected to the ground electrode via one of the two vias, and the other one of the conductor patterns is connected to the ground electrode via the other one of the two vias.