A data processing unit for wirelessly communicating with a plurality of other data processing units, comprising: transmitting means for transmitting data according to communication parameters; receiving means for receiving data from at least two of said other data processing units according to the communication parameters; checking means for check out, according to the data received by the receiving means, if the communication parameters are suited for the radio wave environment; and control means for setting communication parameters suited to the radio wave environment wherein one of the communication parameters is a threshold value used for comparing the qualities of first and second received radio waves, the first received radio wave being currently used in communication of the data processing unit, the second received radio wave being selectable in a hand-over, wherein the receiving means monitors a quality of the second received radio wave as the selectable one, when the difference between the qualities of the first and second radio waves is less than the threshold value, wherein the checking means checks out, while the data processing unit is in communication and according to the result of the hand-over if the threshold value has been set suitable for the radio wave environment. wherein the checking means checks out, when the communication of the data processing unit is discontinued or power source of the data processing unit is turned on and according to the result of a band search for detecting the radio wave that can be received, if communication parameters suitable for the radio wave environment have been set, wherein one of the communication parameters checked out when the communication of the data processing unit is discontinued or power source of he data processing unit is turned on is a waiting time from a momentary discontinuation of the communication till starting the band search next time. transmitting means for transmitting data according to communication parameters; receiving means for receiving data from at least two of said other data processing units according to the communication parameters; checking means for check out, according to the data received by the receiving means, if the communication parameters are suited for the radio wave environment; and control means for setting communication parameters suited to the radio wave environment wherein one of the communication parameters is a threshold value used for comparing the qualities of first and second received radio waves, the first received radio wave being currently used in communication of the data processing unit, the second received radio wave being selectable in a hand-over, wherein the receiving means monitors a quality of the second received radio wave as the selectable one, when the difference between the qualities of the first and second radio waves is less than the threshold value, wherein the checking means checks out, while the data processing unit is in communication and according to the result of the hand-over if the threshold value has been set suitable for the radio wave environment. wherein the checking means checks out, when the communication of the data processing unit is discontinued or power source of the data processing unit is turned on and according to the result of a band search for detecting the radio wave that can be received, if communication parameters suitable for the radio wave environment have been set, wherein one of the communication parameters checked out when the communication of the data processing unit is discontinued or power source of he data processing unit is turned on is a waiting time from a momentary discontinuation of the communication till starting the band search next time.