An X-ray CT imaging apparatus (10;110) comprising: a turning support (20;124;324) that supports an X-ray generator (22;126) and an X-ray detector (24;128) so that the X-ray generator (22;126) and the X-ray detector (24;128) are opposed to each other with a subject sandwiched therebetween; a turning drive mechanism (30;130) including a turning mechanism (32;132) that turns said turning support (20;124;324) about a mechanical turning axis located between said X-ray generator (22;126) and said X-ray detector (24;128) and a turning axis moving mechanism (38;134) that moves said mechanical turning axis in a direction intersecting with an axial direction of said mechanical turning axis; a subject physique setting unit (40;151a) that can set a size of a physique of the subject; and a turning controller (60;151b) that controls said turning mechanism and said turning axis moving mechanism (38;134), wherein when X-ray CT imaging is performed by irradiating the subject with an X-ray generated from said X-ray generator (22;126), said turning axis moving mechanism (38;134) moves said mechanical turning axis in synchronization with turning of said turning support (20;124;324) about said mechanical turning axis using said turning mechanism (32;132), and said turning support (20;124;324) is caused to perform combined motion, which allows said X-ray generator (22;126) and said X-ray detector (24;128) to turn about a center of an X-ray CT imaging region, position control of said turning axis is performed according to the size of the physique of the subject set by said subject physique setting unit (40;151a), a separation distance is defined to be the smaller one of a distance between the center of said X-ray CT imaging region and said X-ray generator and a distance between the center of said X-ray CT imaging region and said X-ray detector; and when said X-ray generator and said X-ray detector are turned around the center of said X-ray CT imaging region, a position of said mechanical turning axis with respect to the center of said X-ray CT imaging region is controlled such that in the case that the set physique of the subject is a first physique said separation distance is larger than in the case that the set physique of the subject is a second physique that is smaller than said first physique according to the size of the physique of the subject set by said subject physique setting unit. a turning support (20;124;324) that supports an X-ray generator (22;126) and an X-ray detector (24;128) so that the X-ray generator (22;126) and the X-ray detector (24;128) are opposed to each other with a subject sandwiched therebetween; a turning drive mechanism (30;130) including a turning mechanism (32;132) that turns said turning support (20;124;324) about a mechanical turning axis located between said X-ray generator (22;126) and said X-ray detector (24;128) and a turning axis moving mechanism (38;134) that moves said mechanical turning axis in a direction intersecting with an axial direction of said mechanical turning axis; a subject physique setting unit (40;151a) that can set a size of a physique of the subject; and a turning controller (60;151b) that controls said turning mechanism and said turning axis moving mechanism (38;134), wherein when X-ray CT imaging is performed by irradiating the subject with an X-ray generated from said X-ray generator (22;126), said turning axis moving mechanism (38;134) moves said mechanical turning axis in synchronization with turning of said turning support (20;124;324) about said mechanical turning axis using said turning mechanism (32;132), and said turning support (20;124;324) is caused to perform combined motion, which allows said X-ray generator (22;126) and said X-ray detector (24;128) to turn about a center of an X-ray CT imaging region, position control of said turning axis is performed according to the size of the physique of the subject set by said subject physique setting unit (40;151a), a separation distance is defined to be the smaller one of a distance between the center of said X-ray CT imaging region and said X-ray generator and a distance between the center of said X-ray CT imaging region and said X-ray detector; and when said X-ray generator and said X-ray detector are turned around the center of said X-ray CT imaging region, a position of said mechanical turning axis with respect to the center of said X-ray CT imaging region is controlled such that in the case that the set physique of the subject is a first physique said separation distance is larger than in the case that the set physique of the subject is a second physique that is smaller than said first physique according to the size of the physique of the subject set by said subject physique setting unit.