PROBLEM TO BE SOLVED: To detect a droplet accurately by suppressing influence of noise.SOLUTION: A droplet detector 1 includes: a light projection element 2 for irradiating light to a droplet passing sight of a drip tube 101 an upper side first light receiving element 3 and a lower side light receiving element 5 for receiving light irradiated by the light projection element 2 and a signal processing part 10. The upper side first light receiving element 3 and the lower side light receiving element 5 are spaced apart in the vertical direction of the drip tube 101. The signal processing part 10 has a differential amplifier 12 to which signals output from the upper first light receiving element 3 and the lower side light receiving element 5 are input.