A traffic information distribution method implemented in a computer which acquires or generates traffic information on a road traffic situation and distributes the traffic information individually to each of in-vehicle terminals installed in vehicles, the method allowing the computer to perform the steps comprising: a traffic information accumulation step of, at the time when the computer acquires or generates the traffic information, including predetermined identification information in the traffic information and accumulating in a storage device the traffic information which includes the predetermined identification information; a distribution request information reception step of receiving distribution request information transmitted from the in-vehicle terminal and containing identification information which is included in reference traffic information the in-vehicle terminal holds at the time when the in-vehicle terminal transmits the distribution request information; and a difference traffic information generation step of generating difference traffic information between the traffic information stored in the storage device and having a same identification information as the identification information included in the reference traffic information contained in the received distribution request information and the traffic information which is to be distributed at the time when the difference traffic information is generated; characterized in that the method further allowing the computer to perform a distribution mode setting step of: calculating a divergence degree between the traffic information stored in the storage device and having the same identification information as the identification information included in the reference traffic information contained in the received distribution request information and the traffic information which is to be distributed, and setting a difference information distribution mode if the divergence degree is less than a predetermined value, and setting an entire information distribution mode if the divergence degree is larger than or equal to the predetermined value, wherein at the distribution mode setting step, the computer: distributes the difference traffic information generated at the difference traffic information generation step to the in-vehicle terminal when the difference information distribution mode is set; and distributes entire information of the traffic information to be distributed to the in-vehicle terminal when the entire information distribution mode is set. a traffic information accumulation step of, at the time when the computer acquires or generates the traffic information, including predetermined identification information in the traffic information and accumulating in a storage device the traffic information which includes the predetermined identification information; a distribution request information reception step of receiving distribution request information transmitted from the in-vehicle terminal and containing identification information which is included in reference traffic information the in-vehicle terminal holds at the time when the in-vehicle terminal transmits the distribution request information; and a difference traffic information generation step of generating difference traffic information between the traffic information stored in the storage device and having a same identification information as the identification information included in the reference traffic information contained in the received distribution request information and the traffic information which is to be distributed at the time when the difference traffic information is generated; characterized in that the method further allowing the computer to perform a distribution mode setting step of: calculating a divergence degree between the traffic information stored in the storage device and having the same identification information as the identification information included in the reference traffic information contained in the received distribution request information and the traffic information which is to be distributed, and setting a difference information distribution mode if the divergence degree is less than a predetermined value, and setting an entire information distribution mode if the divergence degree is larger than or equal to the predetermined value, wherein at the distribution mode setting step, the computer: calculating a divergence degree between the traffic information stored in the storage device and having the same identification information as the identification information included in the reference traffic information contained in the received distribution request information and the traffic information which is to be distributed, and setting a difference information distribution mode if the divergence degree is less than a predetermined value, and setting an entire information distribution mode if the divergence degree is larger than or equal to the predetermined value, wherein at the distribution mode setting step, the computer: distributes the difference traffic information generated at the difference traffic information generation step to the in-vehicle terminal when the difference information distribution mode is set; and distributes entire information of the traffic information to be distributed to the in-vehicle terminal when the entire information distribution mode is set.