A photodetector comprising: a plurality of photodiodes (PD 1, PD 2, PD 3, PD n,... PD N), each generating charges of an amount that is in accordance with the intensity of incident light; and integrating circuits (10 1, 10 2, 10 3, 10 n,... 10 N), said plurality of photodiodes (PD 1, PD 2, PD 3, PD n,... PD N) being disposed on a first substrate, input ends of said integrating circuits (10 1, 10 2, 10 3, 10 n,... 10 N) being disposed on a second substrate, said photodiodes (PD 1, PD 2, PD 3, PD n,... PD N) and said input ends of said integrating circuits (10 1, 10 2, 10 3, 10 n,... 10 N) being electrically connected to each other by said first substrate and said second substrate being bump-connected to each other, said second substrate is bump-connected to a third substrate, each integrating circuit (10 1, 10 2, 10 3, 10 n,... 10 N) includes an amplifier (11 n), having a differential pair input part (T 1, T 2) at the input end side and a drive part (T 5, T 6) at the output end side, and a capacitor and a switch, which are disposed between said input end and said output end of said amplifier (11 n), and each integrating circuit (10 1, 10 2, 10 3, 10 n,... 10 N) is adapted in such a way that, when said switch is opened, charges input into said input end from an above-mentioned photodiode (PD 1, PD 2, PD 3, PD n,... PD N) accumulate in the capacitor, and a voltage that is in accordance with the amount of charges accumulated in said capacitor is output from said output end, said capacitors and said differential pair input parts (T 1, T 2) being disposed on said second substrate, characterized in that said drive parts (T 5, T 6) being disposed on said third substrate. a plurality of photodiodes (PD 1, PD 2, PD 3, PD n,... PD N), each generating charges of an amount that is in accordance with the intensity of incident light; and integrating circuits (10 1, 10 2, 10 3, 10 n,... 10 N), said plurality of photodiodes (PD 1, PD 2, PD 3, PD n,... PD N) being disposed on a first substrate, input ends of said integrating circuits (10 1, 10 2, 10 3, 10 n,... 10 N) being disposed on a second substrate, said photodiodes (PD 1, PD 2, PD 3, PD n,... PD N) and said input ends of said integrating circuits (10 1, 10 2, 10 3, 10 n,... 10 N) being electrically connected to each other by said first substrate and said second substrate being bump-connected to each other, said second substrate is bump-connected to a third substrate, each integrating circuit (10 1, 10 2, 10 3, 10 n,... 10 N) includes an amplifier (11 n), having a differential pair input part (T 1, T 2) at the input end side and a drive part (T 5, T 6) at the output end side, and a capacitor and a switch, which are disposed between said input end and said output end of said amplifier (11 n), and each integrating circuit (10 1, 10 2, 10 3, 10 n,... 10 N) is adapted in such a way that, when said switch is opened, charges input into said input end from an above-mentioned photodiode (PD 1, PD 2, PD 3, PD n,... PD N) accumulate in the capacitor, and a voltage that is in accordance with the amount of charges accumulated in said capacitor is output from said output end, said capacitors and said differential pair input parts (T 1, T 2) being disposed on said second substrate, characterized in that said drive parts (T 5, T 6) being disposed on said third substrate.