The Microwave System for the KEK electron/positron linac is being rejuvenated for the KEKB project. Klystrons are being upgraded and pulse compressors are also being employed to accelerate electrons up to 8 GeV. Because of the beam current and emittance requirements in the KEKB accelerator complex, very stable operation of the microwave source is indispensable. Thirty VXI-based microwave-monitoring stations have been installed to maintain in a better operation condition. PLC's for basic controls are being adopted for new klystron modulators and sub-boosters. A redundant optical switching network is employed to accommodate a higher bandwidth and to eliminate noise from the modulators. Upper-layer software for device controls is being upgraded to enable transparent access to both old and new controllers. Not only the current values, but also statistical values, such as averages and standard deviations, will be served for client programs. Advanced application programs, such as feedback ..