1. A method for acquiring information of a detected object from intensity information of interference fringes of radiation rays that have passed through the detected object, the method comprising the steps of: generating first phase information of the detected object wrapped into a range of 2π from the intensity information of the interference fringes; generating information on an absorption intensity gradient of the detected object from the intensity information of the interference fringes; generating a weighting function on the basis of an absolute value of a gradient in the information on the absorption intensity gradient; and generating second phase information by unwrapping the first phase information by using the weighting function.