A physical quantity distribution detecting apparatus includes a sensor array in which a plurality of unit sensors for sensing physical quantity are two-dimensionally arranged in a matrix; and an analog-to-digital conversion unit that includes a plurality of comparators for comparing an analog signal read from the unit sensor with a reference signal, the analog-to-digital conversion unit converting a digital signal by measuring a period of time or measuring a signal corresponding to the period of time of each comparison output of the plurality of comparators. Each of the plurality of comparators includes at least one capacitor element connected between a signal line and a constant-voltage line.