An image projecting device configured to project an image onto a screen, comprising: an image forming element configured to form an image; a light source configured to generate light to illuminate the image forming element; and an imaging optical system configured to image an image formed by the image forming element on a screen, wherein the image projecting device further comprises: a first prism having: a first transmission surface configured to transmit light generated from the light source therethrough; a reflection curved surface being a curved surface configured to directly reflect light having transmitted through the first transmission surface; a reflection-transmission surface configured to directly reflect light reflected from the reflection curved surface and through a second transmission surface to the image forming element and transmit light reflected from the image forming element and through the second transmission surface therethrough, wherein the reflection-transmission surface is a flat surface, wherein the reflection-transmission surface and the second transmission surface are flat surfaces inclining with respect to each other; and a second prism configured to direct light having transmitted through the reflection-transmission surface of the first prism to the imaging optical system, wherein the second prism has a transmission surface being a flat surface configured to transmit light having transmitted through the reflection-transmission surface of the first prism therethrough and the second prism is arranged such that the transmission surface of the second prism is parallel to the reflection-transmission surface of the first prism. an image forming element configured to form an image; a light source configured to generate light to illuminate the image forming element; and an imaging optical system configured to image an image formed by the image forming element on a screen, wherein the image projecting device further comprises: a first prism having: a first transmission surface configured to transmit light generated from the light source therethrough; a reflection curved surface being a curved surface configured to directly reflect light having transmitted through the first transmission surface; a reflection-transmission surface configured to directly reflect light reflected from the reflection curved surface and through a second transmission surface to the image forming element and transmit light reflected from the image forming element and through the second transmission surface therethrough, wherein the reflection-transmission surface is a flat surface, wherein the reflection-transmission surface and the second transmission surface are flat surfaces inclining with respect to each other; and a second prism configured to direct light having transmitted through the reflection-transmission surface of the first prism to the imaging optical system, wherein the second prism has a transmission surface being a flat surface configured to transmit light having transmitted through the reflection-transmission surface of the first prism therethrough and the second prism is arranged such that the transmission surface of the second prism is parallel to the reflection-transmission surface of the first prism. a first prism having: a first transmission surface configured to transmit light generated from the light source therethrough; a reflection curved surface being a curved surface configured to directly reflect light having transmitted through the first transmission surface; a reflection-transmission surface configured to directly reflect light reflected from the reflection curved surface and through a second transmission surface to the image forming element and transmit light reflected from the image forming element and through the second transmission surface therethrough, wherein the reflection-transmission surface is a flat surface, wherein the reflection-transmission surface and the second transmission surface are flat surfaces inclining with respect to each other; and a first transmission surface configured to transmit light generated from the light source therethrough; a reflection curved surface being a curved surface configured to directly reflect light having transmitted through the first transmission surface; a reflection-transmission surface configured to directly reflect light reflected from the reflection curved surface and through a second transmission surface to the image forming element and transmit light reflected from the image forming element and through the second transmission surface therethrough, wherein the reflection-transmission surface is a flat surface, wherein the reflection-transmission surface and the second transmission surface are flat surfaces inclining with respect to each other; a second prism configured to direct light having transmitted through the reflection-transmission surface of the first prism to the imaging optical system, wherein the second prism has a transmission surface being a flat surface configured to transmit light having transmitted through the reflection-transmission surface of the first prism therethrough and the second prism is arranged such that the transmission surface of the second prism is parallel to the reflection-transmission surface of the first prism.