A linked display system comprising first and second display apparatuses (100, 200), wherein the first display apparatus includes: a first display unit configured to display operation display information; an operation input unit for detecting a position on the operation display information specified by an user operation input; a range setting unit configured to set, upon detection of the user operation input, a predetermined range containing the specified position, the range being narrower than the displayed operation display information; and a first communication unit configured to transmit the predetermined range to the second display apparatus, and the second display apparatus includes: a second communication unit configured to receive the predetermined range from the first display unit; a display information selection unit configured to select optimal reference display information from information about at least one piece of reference display information received from a service server, the optimal display information, which has a different scale and amount of information than the operation display information, is determined according to the predetermined range and the display capacity of the second display apparatus; and a second display unit configured to display the optimal reference display information; wherein the first communication unit is configured to receive from the second display unit a display range of the optimal reference display information displayed in the second display unit and the first display unit is configured to display a reference display frame indicating the display range of the optimal reference display information by superimposing the reference display frame on the operation display information; wherein the range setting unit is further configured to set the reference display frame after movement corresponding to a move operation by the user of the reference display frame on the first display unit as the predetermined range. a first display unit configured to display operation display information; an operation input unit for detecting a position on the operation display information specified by an user operation input; a range setting unit configured to set, upon detection of the user operation input, a predetermined range containing the specified position, the range being narrower than the displayed operation display information; and a first communication unit configured to transmit the predetermined range to the second display apparatus, and the second display apparatus includes: a second communication unit configured to receive the predetermined range from the first display unit; a display information selection unit configured to select optimal reference display information from information about at least one piece of reference display information received from a service server, the optimal display information, which has a different scale and amount of information than the operation display information, is determined according to the predetermined range and the display capacity of the second display apparatus; and a second display unit configured to display the optimal reference display information; wherein the first communication unit is configured to receive from the second display unit a display range of the optimal reference display information displayed in the second display unit and the first display unit is configured to display a reference display frame indicating the display range of the optimal reference display information by superimposing the reference display frame on the operation display information; wherein the range setting unit is further configured to set the reference display frame after movement corresponding to a move operation by the user of the reference display frame on the first display unit as the predetermined range. a second communication unit configured to receive the predetermined range from the first display unit; a display information selection unit configured to select optimal reference display information from information about at least one piece of reference display information received from a service server, the optimal display information, which has a different scale and amount of information than the operation display information, is determined according to the predetermined range and the display capacity of the second display apparatus; and a second display unit configured to display the optimal reference display information; wherein the first communication unit is configured to receive from the second display unit a display range of the optimal reference display information displayed in the second display unit and the first display unit is configured to display a reference display frame indicating the display range of the optimal reference display information by superimposing the reference display frame on the operation display information; wherein the range setting unit is further configured to set the reference display frame after movement corresponding to a move operation by the user of the reference display frame on the first display unit as the predetermined range.