To reduce the quantity of information required for electronic mail communications.

This electronic mail system is provided with a memory 7 for storing electronic mail, input part 1 for preparing new electronic mail on the basis of the electronic mail stored in the memory 7, sentence analytic part 32 for detecting a different part between the electronic mail prepared by the input part 1 and the electronic mail to become the base of this electronic mail, sentence preparing part 33 for preparing transmitting mail, which contains the different part detected by the sentence analytic part 32, and transmitting/ receiving part 6 for transmitting the transmitting mail prepared by the sentence preparing part 33.