A transmission system includes: a first timing signal generation unit; a second timing signal generation unit; a timing adjustment unit; a transmission processing unit; a first valid data generation unit which receives a first timing signal, receives only data according to valid timing of the first timing signal in a first image signal from a process signal to generate a first valid image signal, and receives only data according to valid timing of the first timing signal in a second image signal and a second timing signal from the process signal to output the received second image signal and the received second timing signal; and a second valid data generation unit which receives the second timing signal from the first valid data generation unit and receives only data according to valid timing of the second timing signal in the second image signal to generate a second valid image signal.