In a construction having a radiation tube in an envelope filled with an insulating liquid, a radiation generating apparatus which realizes a miniaturization of the apparatus, an improvement of a withstanding voltage between the envelope and the radiation tube, and a decrease in attenuation amount of the radiation and a radiation imaging apparatus using the radiation generating apparatus are provided. The radiation generating apparatus has an envelope 12 having a first window 27 for transmitting the radiation, a radiation tube 14 enclosed in the envelope 12 and having a second window 19 for transmitting the radiation at a position in opposition to the first window 27, and an insulating liquid 13 filled between the envelope 12 and the radiation tube 14. A solid-state insulating member 28 is placed between the first window 27 and its periphery and the second window 19 and its periphery.