COLD MIRROR FOR HEAD-UP DISPLAY APPARATUS AND HEAD-UP DISPLAY APPARATUS

This invention relates to a cold mirror for a head-up display apparatus and provides a cold mirror that enables suppression of a phenomenon of change in color tone of an image depending on a position from which the image is viewed. This invention also provides a head-up display apparatus including the cold mirror. In a head-up display apparatus 10, display light 20 of an image displayed on a display 16 is reflected by a cold mirror 12 and a reflected image of the image is viewed by a viewer. A relationship between an incident wavelength and a reflection phase difference in the cold mirror 12 is set so that the reflection phase difference falls within a range of 180±60 degrees for an entire visible wavelength range of 420 to 680 nm.