A preview generating section 104 generates preview forming data within a predetermined data size by extracting at least a part of header information and at least a part of a mail body from an electronic mail obtained by a mail obtaining section 102. A cache section 142 caches the preview forming data. A display section 108 displays a preview list on a display device 68 using the preview forming data cached by the cache section 142. When a preview included in the preview list is selected, a command transmitting section 106 requests a server to transmit the electronic mail identified by the selected preview.