A color-separating and -recombining optical system provided between a light source and a projection lens in a projection display, has at least one prism assembly made up of at least two prisms bonded to each other with a bonding layer formed between the prisms. A white light emitted from the light source is divided into red-, green-, and blue-color light components related to primary colors. The light components are modulated by spatial light modulators in accordance with a video signal. The modulated light components are combined and projected onto a screen via the projection lens. The thickness of the bonding layer is varied as thin and thick for optical paths long and short, respectively, from the spatial light modulators to the bonding layer which each modulated light component emitted from the corresponding spatial light modulator reaches.