A medical X-ray imaging system which comprises a solid-state image pick-up device for imaging an X-ray image while moving around a jaw of an examinee, and has at least two imaging modes, wherein a first imaging mode is an imaging mode for CT in dental X-ray photography, and a second imaging mode is an imaging mode for panoramic radiography in dental X-ray photography, wherein the solid-state image pick-up device includes: a photodetecting section having a rectangular photodetecting surface formed by two-dimensionally aligning M*N pixels (M and N are integers not less than 2) including photodiodes respectively, in M rows and N columns; N reading wires each of which is disposed for each of the columns and connected to the photodiodes included in the pixels of the corresponding column via reading switches; a signal reading section which holds voltage values corresponding to charges input through the reading wires and outputs the held voltage values successively; a controlling section which controls opening and closing operations of the reading switches of the respective pixels, and controls the voltage value outputting operation in the signal reading section to output voltage values corresponding to the charges generated in the photodiodes of the respective pixels from the signal reading section; and a scintillator which generates scintillation light in response to an incident X-ray and converts the X-ray image into an optical image, and outputs the optical image to the photodetecting section, and the medical X-ray imaging system further comprises: a rotation controlling section which supports the solid-state image pick-up device rotatably around an axis line perpendicular to the photodetecting surface, and controls a rotation angle of the solid-state image pick-up device so that, in the first imaging mode of the two imaging modes, either a row direction or a column direction of the photodetecting section is along a movement direction of the solid-state image pick-up device, and in the second imaging mode of the two imaging modes, both of the row direction and the column direction of the photodetecting section tilt with respect to the movement direction of the solid-state image pick-up device, wherein in comparison with the first imaging mode, in the second imaging mode, the controlling section makes smaller a reading pixel pitch in frame data based on voltage values output from the signal reading section, makes higher a frame rate which is a number of frame data to be output per unit time, and makes larger the gain which is a ratio of an output voltage value to an input charge amount in the signal reading section. a photodetecting section having a rectangular photodetecting surface formed by two-dimensionally aligning M*N pixels (M and N are integers not less than 2) including photodiodes respectively, in M rows and N columns; N reading wires each of which is disposed for each of the columns and connected to the photodiodes included in the pixels of the corresponding column via reading switches; a signal reading section which holds voltage values corresponding to charges input through the reading wires and outputs the held voltage values successively; a controlling section which controls opening and closing operations of the reading switches of the respective pixels, and controls the voltage value outputting operation in the signal reading section to output voltage values corresponding to the charges generated in the photodiodes of the respective pixels from the signal reading section; and a scintillator which generates scintillation light in response to an incident X-ray and converts the X-ray image into an optical image, and outputs the optical image to the photodetecting section, and a rotation controlling section which supports the solid-state image pick-up device rotatably around an axis line perpendicular to the photodetecting surface, and controls a rotation angle of the solid-state image pick-up device so that, in the first imaging mode of the two imaging modes, either a row direction or a column direction of the photodetecting section is along a movement direction of the solid-state image pick-up device, and in the second imaging mode of the two imaging modes, both of the row direction and the column direction of the photodetecting section tilt with respect to the movement direction of the solid-state image pick-up device, wherein in comparison with the first imaging mode, in the second imaging mode, the controlling section makes smaller a reading pixel pitch in frame data based on voltage values output from the signal reading section, makes higher a frame rate which is a number of frame data to be output per unit time, and makes larger the gain which is a ratio of an output voltage value to an input charge amount in the signal reading section.