1. A medical diagnostic imaging apparatus, comprising: processing circuitry configured to acquire a plurality of first X-ray images chronologically in a first X-ray irradiation area while adjusting an operating condition by feedback control using a statistic of a pixel value of each first X-ray image and a threshold set in advance; and acquire, after acquiring the plurality of first X-ray images, a plurality of second X-ray images chronologically in a second X-ray irradiation area that is narrower than the first X-ray irradiation area while maintaining the adjusted operating condition adjusted at the time of acquiring an acquired first X-ray image of the plurality of first X-ray images.