A microwave-assisted magnetic head provides a high-reliability microwave-assisted magnetic head that reduces effective coercivity by giving microwave energy to a magnetic recording medium in an auxiliary manner and writes a data signal, a head gimbal assembly, and a magnetic recording and reproducing apparatus. A microwave magnetic field generating element is arranged on a trailing shield side or a reproducing head element side with respect to a main magnetic pole that generates a recording magnetic field for writing a data signal into a magnetic recording medium, the microwave magnetic field generating element having a coil configuration in which a plurality of microwave magnetic field generating lines and a return line are formed by a continuous single line.