There is provided with a method of performing in a server apparatus sharing an image to be displayed on a screen with a client terminal, including: updating a part of an image in a frame buffer; generating a first packet which includes first area information indicating a first area updated in the image, a first image which is an image after update in the first area and a sequence number assigned by a sequence number counter and transmitting it; storing a set of the first area information and the sequence number in a storage; receiving a retransmission request including a sequence number from the client terminal; detecting a second area which is not updated in the first image which corresponds to the sequence number included in the retransmission request after the transmission of the first image by referring to the storage; acquiring a second image in the second area from the frame buffer.