To heighten the awareness of traffic safey by putting on the air a watchword for the traffic safety without trouble in the car interior the moment a vehicle starts to move, and reaches a specified speed to lock the door.

A timer switch 3 is fitted to the vicinity of a door lock 2, whereby the moment a vehicle reaches a regulated speed, 20K to lock the door, a power supply is turned on. The power supply time is set about one minute, and during the time, a voice is put on the air from a CD 4 in the car interior. At this time, the CD and a speaker 5 are exclusive use. Further, many watchwords for the traffic sagety or commercial words, or a beautiful tone of a birdy are previously recorded in the CD. By this arrangement, in the case of driving the vehicle again, when it reaches a preset speed, the power supply is turned on to put a voice on the air in the car interior. That is, when the vehicle is driven to move, a watchword for the traffic safey is heard in the car interior. Thus, a satisfactory effect of recognizing the traffic safety can be produced.