An imaging device comprising: a light receiving lens; an imaging element adapted to output event data including two-dimensional point data corresponding to pixels whose brightness has changed when receiving light via the light receiving lens, the two-dimensional point data having specified pixel positions of a plane representing an area imaged by the imaging element; an adjustment mechanism adapted to adjust a focal point of the light receiving lens; a control unit adapted to drive and to control the adjustment mechanism; and a point density calculation unit adapted to calculate, a point density, the point density being defined as an average nearest neighbor distance of the two-dimensional point data of a plurality of the event data in each block provided by dividing the plane into a predetermined number of two-dimensional blocks, the event data being outputted from the imaging element in a predetermined period in a state in which the focal point of the light receiving lens is adjusted by the adjustment mechanism, wherein the point density calculation unit is adapted to calculate the point density by dividing the plane into said predetermined number of blocks, by plotting the two-dimensional point data as points on each of the blocks of the plane, and by determining, as the point density, the average nearest neighbor distance of the point data in each of the blocks based on a nearest neighbor method, and the control unit is adapted to drive and to control the adjustment mechanism to adjust the focal point toward an in-focus position based on a comparison result between the point density currently calculated by the point density calculation unit and the point density previously calculated. a light receiving lens; an imaging element adapted to output event data including two-dimensional point data corresponding to pixels whose brightness has changed when receiving light via the light receiving lens, the two-dimensional point data having specified pixel positions of a plane representing an area imaged by the imaging element; an adjustment mechanism adapted to adjust a focal point of the light receiving lens; a control unit adapted to drive and to control the adjustment mechanism; and a point density calculation unit adapted to calculate, a point density, the point density being defined as an average nearest neighbor distance of the two-dimensional point data of a plurality of the event data in each block provided by dividing the plane into a predetermined number of two-dimensional blocks, the event data being outputted from the imaging element in a predetermined period in a state in which the focal point of the light receiving lens is adjusted by the adjustment mechanism, wherein the point density calculation unit is adapted to calculate the point density by dividing the plane into said predetermined number of blocks, by plotting the two-dimensional point data as points on each of the blocks of the plane, and by determining, as the point density, the average nearest neighbor distance of the point data in each of the blocks based on a nearest neighbor method, and the control unit is adapted to drive and to control the adjustment mechanism to adjust the focal point toward an in-focus position based on a comparison result between the point density currently calculated by the point density calculation unit and the point density previously calculated.