To provide the controller of a signal device capable of suppressing a traffic jam and making automobiles efficiently and safely pass through even in a one-side alternate passing section during construction.

Passing vehicle sensors 3 and 4 detect passing vehicles for respective up and down directions and a CPU 11 computes the numbers of the passing vehicles for the respective directions in prescribed time. Further, the cycle length of a blue signal and a red signal is computed based on the number of passing vehicles during the prescribed time and a cycle ratio for indicating the ratio of the blue signal time of both signal devices is computed from the number of passing vehicles in the up direction and that of the passing vehicles in the down direction. Then, the CPU 11 calculates the blue signal time of an up signal device and a down signal device from the data of the cycle ratio and controls the lighting of the blue signal and the red signal of the up signal device and the down signal device based on the calculated blue signal time. Since the blue signal time is calculated corresponding to the numbers of respective up and down passing vehicles, the vehicles are efficiently made to pass through corresponding to the numbers of up and down passing vehicles and the traffic jam is effectively mitigated.