An image processing device for use with a fine particle sorting device having a detection unit configured to detect a fine particle in fluid flowing inside a flow path, a light source arranged in a downstream side of the detection unit for acquiring an image of the fine particle, and a charging unit configured to apply electric charge to a droplet including the fine particle included in the fluid, the image processing device comprising: a control unit configured to set a light source lighting delay time to control the light source, the light source lighting delay time indicating a time from a time point when a fine particle in fluid is detected by a detection unit until a time point when the light source is turned on for the fine particle included in a droplet to be imaged formed from the fluid; a processing unit configured to identify positional information indicative of a position of the fine particle in an image of the fine particle acquired by an imaging unit in accordance with lighting of the light source at the set light source lighting delay time; and a recording unit configured to record, in a correlated manner, the positional information identified in the processing unit and the light source lighting delay time for a plurality of different light source lighting delay times set by the control unit, wherein the processing unit is configured to calculate a correlation equation between the positional information and the light source lighting delay time for the plurality of different light source lighting delay times recorded in the recording unit and positional information recorded in a manner correlated to each of the plurality of different light source lighting delay times; wherein the processing unit is configured to determine, as a drop delay time, a light source lighting delay time correlated to target positional information that is predetermined positional information indicative of a break-off point, and the drop delay time indicates a time from the time point when the fine particle is detected by the detection unit until the droplet is formed from the fluid containing the fine particle; wherein the control unit is configured to control the charging unit so as to perform charging at the drop delay time determined by the processing unit. a control unit configured to set a light source lighting delay time to control the light source, the light source lighting delay time indicating a time from a time point when a fine particle in fluid is detected by a detection unit until a time point when the light source is turned on for the fine particle included in a droplet to be imaged formed from the fluid; a processing unit configured to identify positional information indicative of a position of the fine particle in an image of the fine particle acquired by an imaging unit in accordance with lighting of the light source at the set light source lighting delay time; and a recording unit configured to record, in a correlated manner, the positional information identified in the processing unit and the light source lighting delay time for a plurality of different light source lighting delay times set by the control unit, wherein the processing unit is configured to calculate a correlation equation between the positional information and the light source lighting delay time for the plurality of different light source lighting delay times recorded in the recording unit and positional information recorded in a manner correlated to each of the plurality of different light source lighting delay times; wherein the processing unit is configured to determine, as a drop delay time, a light source lighting delay time correlated to target positional information that is predetermined positional information indicative of a break-off point, and the drop delay time indicates a time from the time point when the fine particle is detected by the detection unit until the droplet is formed from the fluid containing the fine particle; wherein the control unit is configured to control the charging unit so as to perform charging at the drop delay time determined by the processing unit.