Disclosed are an imaging device, a control method therefor, and an imaging system capable of allowing efficient use by multiple users and achieving improvement of a rate of operation. An imaging device which photoelectrically reads fluorescence or chemiluminescence emitted from an object to image the object includes a control unit which receives first control information for controlling a first function and second control information for controlling a second function from a plurality of external terminals and performs control based on the received first and second control information. The control unit recognizes the execution states of the first function and the second function in each external terminal based on the first and second control information output from each external terminal, restricts simultaneous processing of the first function in the plurality of external terminals, and performs parallel processing of the first function and the second function in the plurality of external terminals.