A digital cordless telephone system for business use composed of a base station and a terminal employing PHS (Personal Handy-Phone System) technology, the base station comprising: a carrier sense means for carrier-sensing nearby radio waves at each predetermined sampling period, configured to determine whether radio wave interference with a communication channel to be used for communication with the terminal is occurring by identifying whether the radio wave is a radio wave of another type of radio system different from PHS or a jamming wave, or by combining identifying whether the radio wave is a radio wave modulated by a modulation method different from a PHS modulation method with the identifying whether the radio wave is a radio wave of another type of radio system or a jamming wave, and configured to output a result of monitoring whether radio wave interference with a communication channel to be used for communication with the terminal is occurring as a carrier sense result; a communication channel management means for managing ranking of communication channels by ranking usable communication channels to be allocated to communication with the terminal as an allocation priority order based on the carrier sense result output from the carrier sense means; and a communication channel switching control means for, when a request for acquiring a communication channel to be used for communication with the terminal or a request for switching to another communication channel is made, preferentially selecting and allocating a communication channel being high in the ranking among the communication channels whose ranking is managed by the communication channel management means, wherein the carrier sense means is configured to use, as a monitor channel being a time for periodically carrier-sensing nearby radio waves, any one of a first channel being an unused time slot not in use due to PHS frame structural reasons or being, in addition to the unused time slot, a receiving time slot of a communication channel in an idle state unallocated to communication among communication channels for communication with the terminal, a second channel placed for, when a dedicated base station for carrier-sensing nearby radio waves is included, receiving the carrier sense result transmitted from the dedicated base station at each sampling period, and a third channel placed for, when a terminal in an idle state being not in communication among the terminals located nearby carrier-senses nearby radio waves at an arbitrary timing, receiving the carrier sense result transmitted from the terminal at each sampling period. a carrier sense means for carrier-sensing nearby radio waves at each predetermined sampling period, configured to determine whether radio wave interference with a communication channel to be used for communication with the terminal is occurring by identifying whether the radio wave is a radio wave of another type of radio system different from PHS or a jamming wave, or by combining identifying whether the radio wave is a radio wave modulated by a modulation method different from a PHS modulation method with the identifying whether the radio wave is a radio wave of another type of radio system or a jamming wave, and configured to output a result of monitoring whether radio wave interference with a communication channel to be used for communication with the terminal is occurring as a carrier sense result; a communication channel management means for managing ranking of communication channels by ranking usable communication channels to be allocated to communication with the terminal as an allocation priority order based on the carrier sense result output from the carrier sense means; and a communication channel switching control means for, when a request for acquiring a communication channel to be used for communication with the terminal or a request for switching to another communication channel is made, preferentially selecting and allocating a communication channel being high in the ranking among the communication channels whose ranking is managed by the communication channel management means, wherein the carrier sense means is configured to use, as a monitor channel being a time for periodically carrier-sensing nearby radio waves, any one of a first channel being an unused time slot not in use due to PHS frame structural reasons or being, in addition to the unused time slot, a receiving time slot of a communication channel in an idle state unallocated to communication among communication channels for communication with the terminal, a second channel placed for, when a dedicated base station for carrier-sensing nearby radio waves is included, receiving the carrier sense result transmitted from the dedicated base station at each sampling period, and a third channel placed for, when a terminal in an idle state being not in communication among the terminals located nearby carrier-senses nearby radio waves at an arbitrary timing, receiving the carrier sense result transmitted from the terminal at each sampling period.