A transmission system comprising a first information processing apparatus and a second information processing apparatus and transmitting information from the first information processing apparatus to the second information processing apparatus, the first information processing apparatus comprising: a material transmitter that uploads material data to a third information processing apparatus; an operation acquiring unit that acquires an operation by a user and outputs operation information indicating the acquired operation; a transmission side controller that causes a transmission side display unit to display the material data and changes how the material data is displayed in accordance with the operation by the user; and a control data generating unit that generates control data containing the operation information; wherein the control data generating unit incorporates an end instruction into the control data when communication with the second information processing apparatus is ended; and the second information processing apparatus comprising: a material receiver that downloads the material data from the third information processing apparatus; a reception side controller that causes a reception side display unit to display the downloaded material data and changes how the material data is displayed in accordance with the operation information acquired by the first information processing apparatus; characterized in that: the control data generating unit incorporates reference permission information into the control data when the material data is made referable even after the communication is ended, the control data processing unit gives the end instruction and the reference permission information contained in the control data to the reception side controller, and the reception side controller deletes the downloaded material data when the end instruction is given, but does not execute deletion of the downloaded material data when the reference permission information is given the first information processing apparatus comprising: a material transmitter that uploads material data to a third information processing apparatus; an operation acquiring unit that acquires an operation by a user and outputs operation information indicating the acquired operation; a transmission side controller that causes a transmission side display unit to display the material data and changes how the material data is displayed in accordance with the operation by the user; and a control data generating unit that generates control data containing the operation information; wherein the control data generating unit incorporates an end instruction into the control data when communication with the second information processing apparatus is ended; and a material transmitter that uploads material data to a third information processing apparatus; an operation acquiring unit that acquires an operation by a user and outputs operation information indicating the acquired operation; a transmission side controller that causes a transmission side display unit to display the material data and changes how the material data is displayed in accordance with the operation by the user; and a control data generating unit that generates control data containing the operation information; wherein the control data generating unit incorporates an end instruction into the control data when communication with the second information processing apparatus is ended; and the second information processing apparatus comprising: a material receiver that downloads the material data from the third information processing apparatus; a reception side controller that causes a reception side display unit to display the downloaded material data and changes how the material data is displayed in accordance with the operation information acquired by the first information processing apparatus; a material receiver that downloads the material data from the third information processing apparatus; a reception side controller that causes a reception side display unit to display the downloaded material data and changes how the material data is displayed in accordance with the operation information acquired by the first information processing apparatus; characterized in that: the control data generating unit incorporates reference permission information into the control data when the material data is made referable even after the communication is ended, the control data processing unit gives the end instruction and the reference permission information contained in the control data to the reception side controller, and the reception side controller deletes the downloaded material data when the end instruction is given, but does not execute deletion of the downloaded material data when the reference permission information is given the control data generating unit incorporates reference permission information into the control data when the material data is made referable even after the communication is ended, the control data processing unit gives the end instruction and the reference permission information contained in the control data to the reception side controller, and the reception side controller deletes the downloaded material data when the end instruction is given, but does not execute deletion of the downloaded material data when the reference permission information is given