A 100-MeV high-intensity (20 mA CW) proton linac is being built in the KAERI (Korea Atomic Energy Research Institute), Korea. Beam diagnostic system for the machine require to include BCMs (Beam Current Monitors), BPPMs (Beam Position and Phase Monitors), and other devices. BCMs are of special importance for high-intensity proton linacs, since the control of beam loss is critical. They should have high stability and resolution better than 5E-4. BPPMs are for measuring beam position and phase (w.r.t RF) simultaneously, that are crucial for the successful commissioning and operation of the accelerator. All diagnostic devices are required to operate both in CW and pulsed (several ms) modes. Pulsed mode operation is useful when machine tuning and commissioning. In this article, we report the developmental status of beam diagnostic devices for the KOMAC accelerator, with detailed description on the BPPM PU design.