1. ABSTRACTIt is mandatory to equip DRL (Daytime Running Light) with cars in high-altitude countries such as Canada and Nordic countries. These days safety effects of the DRL system has been confirmed, leading to voluntary standard equipment in the U.S. where DRL is not mandatory yet.We have supplied DRL to the automotive market since 1990. Our DRL is mainly a power resistor type which requires a resistor as a system component and an ECU (Electrical Control Unit). In order to accelerate the adoption of the DRL as standard equipment, we have determined that it needs low man power for installation and be a system of small size. With this in mindwe started the development of the PWM - type (Pulse Width Modulation) DRL, which doesn't require a power resistor.Other vehicle electronics, however, near a PWM - type device may be susceptible to switching noise, i.e., radio frequency noise effects.In this paper, we will report on the PWM - type DRL which has achieved: 1. RF noise: -86 dBm 2. Heat from output power device: 28 °C 3. System cost: 23% down from our current DRL through countermeasures for RF noise by slowing the output wave edges, that is, increasing the switching time, and for heat generation by use of low on-resistance FET, etc.