According to one embodiment, an X-ray imaging apparatus includes an X-ray generation unit, an X-ray collimator, a dose detection unit, and a dose reduction rate calculation unit. The X-ray generation unit irradiates the object with X-rays. The X-ray collimator limits an X-ray irradiation range of the X-ray generation unit. The dose detection unit detects the X-rays that have passed through the X-ray collimator. The dose reduction rate calculation unit calculates a reduction rate of an exposure dose of the object based on a value detected by the dose detection unit in X-ray imaging before the X-ray irradiation range is limited by the X-ray collimator and a value detected by the dose detection unit in X-ray imaging after the X-ray irradiation range is limited by the X-ray collimator.