A solid-state image pickup device for generating image data according to an incident X-ray image, comprising: a first substrate having a first pixel array with MxNA, M and NA being each an integer not less than 2, pixels each including a photodiode that are two-dimensionally arrayed in M rows and NA columns; a second substrate having a second pixel array with MxNB, NB being an integer not less than 2 and smaller than NA, pixels each including a photodiode that are two-dimensionally arrayed in M rows and NB columns, where the first substrate is arranged side by side with the second substrate, the first column of the second pixel array being arranged side by side with the NA-th column of the first pixel array; (NA+NB) readout wiring lines disposed for each respective column of the first and second pixel arrays (10A, 10B), and each connected to the photodiode included in the pixel of a corresponding column via a readout switch; a signal output section for holding a voltage value according to an amount of charge input through the readout wiring line (LOj), and outputting the held voltage value; a scintillator (4A, 4B) for generating scintillation light in response to incident X-rays to convert the X-ray image into an optical image, and outputting the optical image to the first and second pixel arrays (10A, 10B), wherein the signal output section is configured to output digital values corresponding to n respective columns from the first column to the n-th column, wherein 2≤n<NA, of the first pixel array, sequentially, and in parallel with this output, outputs the digital values corresponding to the respective columns from the (n+1)-th column of the first pixel array through the NA-th column and the first column of the second pixel array to the NB-th column, sequentially. a first substrate having a first pixel array with MxNA, M and NA being each an integer not less than 2, pixels each including a photodiode that are two-dimensionally arrayed in M rows and NA columns; a second substrate having a second pixel array with MxNB, NB being an integer not less than 2 and smaller than NA, pixels each including a photodiode that are two-dimensionally arrayed in M rows and NB columns, where the first substrate is arranged side by side with the second substrate, the first column of the second pixel array being arranged side by side with the NA-th column of the first pixel array; (NA+NB) readout wiring lines disposed for each respective column of the first and second pixel arrays (10A, 10B), and each connected to the photodiode included in the pixel of a corresponding column via a readout switch; a signal output section for holding a voltage value according to an amount of charge input through the readout wiring line (LOj), and outputting the held voltage value; a scintillator (4A, 4B) for generating scintillation light in response to incident X-rays to convert the X-ray image into an optical image, and outputting the optical image to the first and second pixel arrays (10A, 10B), wherein the signal output section is configured to output digital values corresponding to n respective columns from the first column to the n-th column, wherein 2≤n<NA, of the first pixel array, sequentially, and in parallel with this output, outputs the digital values corresponding to the respective columns from the (n+1)-th column of the first pixel array through the NA-th column and the first column of the second pixel array to the NB-th column, sequentially.