The present invention provides a PCI bus controller to prevent system down caused by a PCI bus fault and to enable a PCI device driver to handle all PCI bus faults. A bus signal controlling portion controls a transaction with a PCI device on a PCI bus according to a PCI bus protocol, treats the PCI bus as in a degradation state by lighting up a bus fault indicator when a bus fault is detected, and accepts a request of instructing the PCI device. A configuration portion has the bus fault indicator, updates a configuration register, and sends a reply transaction to an inbound controller portion. An arbitration portion arbitrates for a PCI bus and masks a request of use a bus from PCI device when the bus is in a degradation state.