PURPOSE: To call a driver's attention running on a main road to a car to be joined, to reduce car accidents occured in a juncture point and to smooth join by displaying the presence of the car to be joined running the join road on the main line.

CONSTITUTION: A detection means 5 is located near the juncture point of a join road 1, detecting the presence of a vehicle 3 joining a main road 2 from the join road 1 and outputting detection information. In short, a light emitting section 51 and a light receiving section 52 for an infrared ray sensor are placed opposite each other on both ends near the juncture point of the join road 1. The vehicle 3 running on the join road 1 approaches a detection means 5, the means 5 detects the presence of the vehicle 3 by blocking the infrared ray emitted from the light emitting section 51 by the vehicle 3. The detected detection information is outputted after being changed into an electric signal. A display means 6 is located on the main road 2, displaying the detection information outputted by the detection means 5. Therefore, a vehicle 3 running on the main road 2 can confirm the presence of the vehicle 3 joining from the join road 1 to the main road 2 based on the display.