A control timing synchronization method that is executed by a first optical transmission apparatus that acts as a transmitting end in a wavelength path, and a second optical transmission apparatus that receives in the wavelength path, an optical signal from the first optical transmission apparatus, the control timing synchronization method comprising: the first optical transmission apparatus: superimposing on a main signal and transmitting, information for giving notification of control process details, waiting for a first period after transmitting the information, superimposing on the main signal and transmitting after waiting for the first period, a message for giving notification of control start timing, waiting for a second period after transmitting the message, and switching after waiting for the second period, a process of the first optical transmission apparatus to a process corresponding to the control process details; and the second optical transmission apparatus: acquiring (S11, S21) the information superimposed on the main signal and transmitted from the first optical transmission apparatus, waiting (S13, S23) until detection of the message superimposed on the main signal and transmitted from the first optical transmission apparatus, when a process is present (S12, S22) that is to be executed by the second optical transmission apparatus based on the information, waiting (S14, S24) for the second period when the message is detected while waiting (S13, S23) for the detection of the message, and executing (S15, S25) after waiting for the second period, a process corresponding to the information. the first optical transmission apparatus: superimposing on a main signal and transmitting, information for giving notification of control process details, waiting for a first period after transmitting the information, superimposing on the main signal and transmitting after waiting for the first period, a message for giving notification of control start timing, waiting for a second period after transmitting the message, and switching after waiting for the second period, a process of the first optical transmission apparatus to a process corresponding to the control process details; and superimposing on a main signal and transmitting, information for giving notification of control process details, waiting for a first period after transmitting the information, superimposing on the main signal and transmitting after waiting for the first period, a message for giving notification of control start timing, waiting for a second period after transmitting the message, and switching after waiting for the second period, a process of the first optical transmission apparatus to a process corresponding to the control process details; and the second optical transmission apparatus: acquiring (S11, S21) the information superimposed on the main signal and transmitted from the first optical transmission apparatus, waiting (S13, S23) until detection of the message superimposed on the main signal and transmitted from the first optical transmission apparatus, when a process is present (S12, S22) that is to be executed by the second optical transmission apparatus based on the information, waiting (S14, S24) for the second period when the message is detected while waiting (S13, S23) for the detection of the message, and executing (S15, S25) after waiting for the second period, a process corresponding to the information. acquiring (S11, S21) the information superimposed on the main signal and transmitted from the first optical transmission apparatus, waiting (S13, S23) until detection of the message superimposed on the main signal and transmitted from the first optical transmission apparatus, when a process is present (S12, S22) that is to be executed by the second optical transmission apparatus based on the information, waiting (S14, S24) for the second period when the message is detected while waiting (S13, S23) for the detection of the message, and executing (S15, S25) after waiting for the second period, a process corresponding to the information.