A particle size measuring apparatus configured to measure a size of a particle, comprising: a first light source configured to emit a parallel beam toward a sample containing particles; an image capturing apparatus disposed to approximately face the first light source with the sample disposed therebetween and configured to capture a scattered light image of the sample; a second light source configured to emit light toward the sample from a direction matching an optical axis of the image capturing apparatus so that a particle shadow image can be captured by the image capturing apparatus; said image capturing apparatus configured to capture said particle shadow image; and an image analyzing unit configured to analyze the image captured by the image capturing apparatus; wherein the image capturing apparatus and the first light source are in prescribed arrangement so as to approximately face each other so that an image of scattered light of the parallel beam incident on particles and scattered at a prescribed angle (θth) or smaller is captured by the image capturing apparatus; wherein the image analyzing unit is configured to calculate a particle size and a particle position on the basis of the scattered light image captured by the image capturing apparatus; wherein the prescribed arrangement indicates that an optical axis of the image capturing apparatus and a direction of the parallel beam cross each other at the prescribed angle or smaller; wherein the prescribed angle (θth) is determined as a threshold of a scattering angle at which the particle size can be identified from a difference in intensity of scattered light in particles; wherein the image analyzing unit is configured to further receive the particle shadow image indicating a shape of a particle and calculate a particle size and a particle position from the acquired particle shadow image; and wherein the image analyzing unit is further configured to identify particles having matching positions in the scattered light image and the particle shadow image, and for an identified particle, select and output the particle size calculated from the particle shadow image when the particle size calculated from the particle shadow image is equal to or smaller than a prescribed size and select and output the particle size calculated from the scattered light image in other cases. a first light source configured to emit a parallel beam toward a sample containing particles; an image capturing apparatus disposed to approximately face the first light source with the sample disposed therebetween and configured to capture a scattered light image of the sample; a second light source configured to emit light toward the sample from a direction matching an optical axis of the image capturing apparatus so that a particle shadow image can be captured by the image capturing apparatus; said image capturing apparatus configured to capture said particle shadow image; and an image analyzing unit configured to analyze the image captured by the image capturing apparatus; wherein the image capturing apparatus and the first light source are in prescribed arrangement so as to approximately face each other so that an image of scattered light of the parallel beam incident on particles and scattered at a prescribed angle (θth) or smaller is captured by the image capturing apparatus; wherein the image analyzing unit is configured to calculate a particle size and a particle position on the basis of the scattered light image captured by the image capturing apparatus; wherein the prescribed arrangement indicates that an optical axis of the image capturing apparatus and a direction of the parallel beam cross each other at the prescribed angle or smaller; wherein the prescribed angle (θth) is determined as a threshold of a scattering angle at which the particle size can be identified from a difference in intensity of scattered light in particles; wherein the image analyzing unit is configured to further receive the particle shadow image indicating a shape of a particle and calculate a particle size and a particle position from the acquired particle shadow image; and wherein the image analyzing unit is further configured to identify particles having matching positions in the scattered light image and the particle shadow image, and for an identified particle, select and output the particle size calculated from the particle shadow image when the particle size calculated from the particle shadow image is equal to or smaller than a prescribed size and select and output the particle size calculated from the scattered light image in other cases.