An optical signal division transmission system in which an input optical signal is divided into N parts (termed as “N-part optical signals”) and transmitted at a transmission rate of 1/N, wherein an additional optical wave path is provided separately from an optical wave paths for transmitting said N-part optical signals, and even if a malfunction occurs in any one of said optical wave paths for transmitting said N-part optical signals, transmission of said N-part optical signals is continued, using said additional optical wave path.