A traffic signal state detection apparatus, installed on a host vehicle, comprising: a wireless communication apparatus as a first traffic signal information obtaining part configured to obtain first traffic signal information from a road side apparatus as a first infrastructure, the first traffic signal information representing a change in a light state of a traffic signal in time series, the traffic signal being located ahead of the most vehicle; and a first output process part configured to calculate, based on the first traffic signal information obtained by the first traffic signal information obtaining part, a first remaining time before a timing when the light state of the traffic signal is to be changed from a current predetermined first state to a second predetermined state that is different from the first state, and generate a first output demand for outputting the calculated first remaining time, characterized by an optical communication apparatus as a second traffic signal information obtaining part configured to obtain second traffic signal information from a road side apparatus as a second infrastructure that is different from the first infrastructure, the second traffic signal information representing the change in the light state of the traffic signal in time series; a second output process part configured to calculate, based on the second traffic signal information obtained by the second traffic signal information obtaining part, a second remaining time before the timing when the light state of the traffic signal is to be changed from the current predetermined first state to the second predetermined state, and generate a second output demand for outputting the calculated second remaining time; and an output part configured to output one of the first and second remaining times wherein the remaining time related to one of the first and second output demand that is continuously generated from the earlier time point is selected for output. a wireless communication apparatus as a first traffic signal information obtaining part configured to obtain first traffic signal information from a road side apparatus as a first infrastructure, the first traffic signal information representing a change in a light state of a traffic signal in time series, the traffic signal being located ahead of the most vehicle; and a first output process part configured to calculate, based on the first traffic signal information obtained by the first traffic signal information obtaining part, a first remaining time before a timing when the light state of the traffic signal is to be changed from a current predetermined first state to a second predetermined state that is different from the first state, and generate a first output demand for outputting the calculated first remaining time, characterized by an optical communication apparatus as a second traffic signal information obtaining part configured to obtain second traffic signal information from a road side apparatus as a second infrastructure that is different from the first infrastructure, the second traffic signal information representing the change in the light state of the traffic signal in time series; a second output process part configured to calculate, based on the second traffic signal information obtained by the second traffic signal information obtaining part, a second remaining time before the timing when the light state of the traffic signal is to be changed from the current predetermined first state to the second predetermined state, and generate a second output demand for outputting the calculated second remaining time; and an output part configured to output one of the first and second remaining times wherein the remaining time related to one of the first and second output demand that is continuously generated from the earlier time point is selected for output.