A particle sorting device for detecting bubbles or foreign substances in particle-containing droplets including a judgment unit configured to judge whether or not captured image information including captured droplet image information about a brightness of an image of particle-containing droplets captured after discharge from an orifice has changed with respect to previously-set reference image information including reference droplet image information about a brightness of an image of droplets captured after discharge from the orifice , characterized in that the reference image information includes the reference droplet image information and reference background image information about a brightness of an image of a reference background other than the droplets, whose peak brightness value, being a brightness value at which a number of pixels of the image of the reference background is maximized, is higher than a peak brightness value, being a brightness value at which a number of pixels of the image of droplets is maximized, of the reference droplet image information , and the captured image information includes the captured droplet image information and captured background image information about a brightness of an image of a captured background other than the droplets, whose peak brightness value, being a brightness value at which a number of pixels of the image of the captured background is maximized, is higher than a peak brightness value, being a brightness value at which a number of pixels of the image of particle-containing droplets is maximized, of the captured droplet image information , and the judgment unit is configured to judge, by judging whether or not the peak brightness value of the captured droplet image information is higher than the peak brightness value of the reference droplet image information , whether or not the bubbles or foreign substances are contained in the particle-containing droplets. the reference image information includes the reference droplet image information and reference background image information about a brightness of an image of a reference background other than the droplets, whose peak brightness value, being a brightness value at which a number of pixels of the image of the reference background is maximized, is higher than a peak brightness value, being a brightness value at which a number of pixels of the image of droplets is maximized, of the reference droplet image information , and the captured image information includes the captured droplet image information and captured background image information about a brightness of an image of a captured background other than the droplets, whose peak brightness value, being a brightness value at which a number of pixels of the image of the captured background is maximized, is higher than a peak brightness value, being a brightness value at which a number of pixels of the image of particle-containing droplets is maximized, of the captured droplet image information , and the judgment unit is configured to judge, by judging whether or not the peak brightness value of the captured droplet image information is higher than the peak brightness value of the reference droplet image information , whether or not the bubbles or foreign substances are contained in the particle-containing droplets. <EOS>