Recent automobile development has led to the installation of rearview cameras or electronic mirrors that could display a rearview image to the driver through a monitor in the driver’s seat and it expected to provide drivers with higher spatial cognition. In this research, we clarify the magnification function that allows optimal cognition of the rear approaching vehicles for drivers. We conduct the experiment introducing Camera monitor system under the same size and location constraints that traditional rearview mirrors face. We use a simple driving simulator and provide participants with a wide rearview by changing the magnification according to the viewing angle. Participants estimate the distance from approaching vehicles that change lanes and press the button. We recorded the distance the button was pressed and a subjective evaluation questionnaire. We analyzed from the point of view that it is safer to perceive the vehicle to vehicle distance to be closer than its actual distance. It was revealed that a pattern that follows the downward convex with no magnification region and a linear function without no magnification region led to the safest presentation of the vehicle to vehicle distance. It was also confirmed that some subjective evaluations of these patterns were higher. In addition, the presentation difference of the vehicle to vehicle distance between one function and the function that is no magnification could be estimated by a model using the least-squares method.