A transmission device includes: a calculation unit to detect abnormal traffic based on a traffic volume collected for the route and to calculate a traffic increase/decrease time and a traffic increase/decrease volume of the abnormal traffic; a normal prediction graph generation unit to generate a normal prediction graph based on the traffic volume in normal time in which the abnormal traffic is not detected; a prediction graph generation unit to generate an abnormal prediction graph based on the traffic increase/decrease time and the traffic increase/decrease volume of the abnormal traffic in detection of the abnormal traffic; an order determination unit to determine a line order that is a priority order of line allocation for the route based on the normal prediction graph or the abnormal prediction graph; and an optimization unit to determine lines that are to be allocated to the route based on the line order.