A data transfer method used in a mobile communication system including a plurality of first wireless base stations that perform communication with a mobile communication device based on a first communication standard and a second wireless base station that performs communication with the mobile communication device based on a second communication standard that has a speed lower than the speed of the first communication standard, characterised by the data transfer method comprising: a first step of receiving, by a base station control unit, a choice selected by a user from among a first choice, a second choice, and a third choice; a second step of detecting, by the base station control unit, the mobile communication device that is receiving first data from a delivery server through any one of the first wireless base stations and is approaching the second wireless base station; when the mobile communication device is detected in the second step, a third step of: if the first choice is received as the choice in the first step, generating, in a data conversion storage server, second data by applying first image processing of lowering image quality to a second portion that is posterior to a first portion of the first data, the first portion having already been sent to the mobile communication device, if the second choice is received as the choice in the first step, generating, by the data conversion storage server, third data by applying second image processing of removing moving images from the second portion, and if the third choice is received as the choice in the first step, storing the second portion as fourth data in the data conversion storage server; and when the second data or the third data is generated in the third step, a fourth step of stopping, by the base station control unit, the transfer of the first data and sending the second data or the third data to the mobile communication device. a first step of receiving, by a base station control unit, a choice selected by a user from among a first choice, a second choice, and a third choice; a second step of detecting, by the base station control unit, the mobile communication device that is receiving first data from a delivery server through any one of the first wireless base stations and is approaching the second wireless base station; when the mobile communication device is detected in the second step, a third step of: if the first choice is received as the choice in the first step, generating, in a data conversion storage server, second data by applying first image processing of lowering image quality to a second portion that is posterior to a first portion of the first data, the first portion having already been sent to the mobile communication device, if the second choice is received as the choice in the first step, generating, by the data conversion storage server, third data by applying second image processing of removing moving images from the second portion, and if the third choice is received as the choice in the first step, storing the second portion as fourth data in the data conversion storage server; and if the first choice is received as the choice in the first step, generating, in a data conversion storage server, second data by applying first image processing of lowering image quality to a second portion that is posterior to a first portion of the first data, the first portion having already been sent to the mobile communication device, if the second choice is received as the choice in the first step, generating, by the data conversion storage server, third data by applying second image processing of removing moving images from the second portion, and if the third choice is received as the choice in the first step, storing the second portion as fourth data in the data conversion storage server; and when the second data or the third data is generated in the third step, a fourth step of stopping, by the base station control unit, the transfer of the first data and sending the second data or the third data to the mobile communication device.