In one embodiment, a data generating apparatus generates data including an irradiation amount of a beam in each pixel for an energy beam writing apparatus. The data generating apparatus includes a target irradiation amount calculating section configured to calculate a first irradiation amount in each pixel, an irradiation amount rounding section configured to round the first irradiation amount based on an irradiation amount control unit and calculate a second irradiation amount, a difference calculating section configured to calculate a first difference between the first irradiation amount and the second irradiation amount, a difference sum calculating section configured to calculate a sum of the first differences in a first group of a plurality of adjacent pixels, and an allocating section configured to allocate an irradiation amount based on the irradiation amount control unit and the sum to a pixel in the first group.