1. An X-ray CT apparatus comprising: an X-ray source configured to irradiate an X-ray while rotating around an object to be examined; an X-ray detector disposed facing the X-ray source placing the object therebetween, configured to detect the X-ray dose transmitted through the object; image reconstruction means configured to reconstruct a tomographic image of the object based on the detected X-ray dose; display means configured to display the tomographic image, characterized in further comprising: X-ray tube current modulation pattern calculation means configured to calculate the X-ray tube current modulation pattern based on a 3-dimensional model of the object calculated based on a scanogram image of the object; start-up shape acquisition means configured to acquire a start-up shape of the CT values or the CT value time difference in a predetermined region of the object after injecting contrast agent into the object; time contrast curve prediction means configured to predict a time contrast curve indicating time series variation of the contrast in a diagnostic region of the object with respect to each slice position upon scanning, based on the start-up shape of the acquired CT values or the CT value time difference; object 3-dimensional model modification means configured to modify the 3-dimensional model of the object based on the predicted time contrast curve; and X-ray tube current modulation pattern modification means configured to modify the X-ray tube current modulation pattern based on the modified object 3-dimensional model.