u03b8 r d holds as shown in fig3 the whole cross section of the human body 10 is contained in the field of the detector 12 therefore an optimum value of the angle u03b8 may be determined by accordingly if the width r of the half of the detector 12 is keyed from the keyboard 42 into the data processing circuit 40 the data processing circuit 40 calculates the angle u03b8 by using the equation 2 and supplies the result of the calculation through the interface circuit 46 to the motor driving section 48 thereby to rotate the motor 26 then the y shaped arm 16 is rotated in the b direction in fig1 to set up u03b8 by the above mentioned method an optimum field can always be obtained after the distance d and the angle u03b8 are selected the motor 36 is rotated and the data obtained by the detector 12 is supplied to the data processing circuit 40 through the interface circuit 38 in the data processing circuit 40 the tomogram is reconstructed on the basis of the data and the reconstructed tomogram is displayed by the display section 44 as shown in fig2 when the detector is rotated with an inclination of the detecting surface 50 at an angle u03b8 with respect to the tangential line the data of the picture elements on the cross sectional area in all the directions can not be obtained thus the true reconstruction can not be conducted to solve this problem.