To provide an inexpensive powder detector of high sensitivity.

The powder detector for detecting at least one of the presence or amount of powder 33 passing through a definite region in a cylinder 32 such as a duct or the like is equipped with two light sources 34 and 35 for irradiating the inside of the cylinder 32 with light, two light detectors 36 and 37 installed at respective positions where emitted light 38 and emitted light 39 pass through the cylinder 32 so as to be incident and a signal processing circuit 25 having a means for detecting changes in output voltages of the light detectors 36 and 37 and detecting the number of times exceeding a definite threshold in the change quantity of the output voltage of the means where emission directions of two light sources 34 and 35 are not parallel to each other to make the emitted light 38 and 39 from those light sources irradiate almost the same part 40 in the cylinder 32.

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