A particle analysis apparatus comprising a configuration to analyze particles in a sample solution based at least on flow cytometry, the particle analysis apparatus comprising: a flow cell having a flow channel for flowing a sample solution comprising particles to be analyzed; a light source device for emitting an irradiation light for said flow cytometry, wherein the light source device comprises a light emitting diode as a light source; an optical system for irradiating the irradiation light on an irradiation segment in the flow channel, wherein the optical system comprises a mask member having a through-hole to form a cross sectional shape of the irradiation light and only the irradiation light that passed through the through-hole is irradiated on the irradiation segment in the flow channel, wherein the through-hole of the mask member has a rectangular opening shape, and wherein the mask member is arranged such that a direction of the long side of the rectangular opening shape is perpendicular to the flow direction of the flow channel; and a light receiving device for detecting the light obtained by irradiating the irradiation light on the irradiation segment; characterized in that an electrode formed on a light extraction surface of the light emitting diode mainly comprises a plurality of electric conductor lines arranged in parallel to each other, and the irradiation light contains a high intensity part and a low intensity part, the low intensity part being caused by the electrode, where the high intensity part and the low intensity part are alternating in a parallel manner due to the parallel arrangement of the plurality of electric conductor lines, the light emitting diode is disposed such that a longitudinal direction of the plurality of electric conductor lines arranged in parallel to each other is parallel to the direction of the long side of the rectangular opening shape of the mask member, and, thereby, such that the longitudinal direction of of the plurality of electric conductor lines arranged in parallel to each other is perpendicular to the flow direction of the flow channel, and the irradiation light passed through the through-hole is irradiated on the irradiation segment in the flow channel such that the flow of the sample solution comprising the particles in the flow channel of the flow cell is passing alternatingly through the high intensity part and the low intensity part of the irradiation light irradiated on the irradiation segment. a flow cell having a flow channel for flowing a sample solution comprising particles to be analyzed; a light source device for emitting an irradiation light for said flow cytometry, wherein the light source device comprises a light emitting diode as a light source; an optical system for irradiating the irradiation light on an irradiation segment in the flow channel, wherein the optical system comprises a mask member having a through-hole to form a cross sectional shape of the irradiation light and only the irradiation light that passed through the through-hole is irradiated on the irradiation segment in the flow channel, wherein the through-hole of the mask member has a rectangular opening shape, and wherein the mask member is arranged such that a direction of the long side of the rectangular opening shape is perpendicular to the flow direction of the flow channel; and wherein the optical system comprises a mask member having a through-hole to form a cross sectional shape of the irradiation light and only the irradiation light that passed through the through-hole is irradiated on the irradiation segment in the flow channel, wherein the through-hole of the mask member has a rectangular opening shape, and wherein the mask member is arranged such that a direction of the long side of the rectangular opening shape is perpendicular to the flow direction of the flow channel; and a light receiving device for detecting the light obtained by irradiating the irradiation light on the irradiation segment; characterized in that an electrode formed on a light extraction surface of the light emitting diode mainly comprises a plurality of electric conductor lines arranged in parallel to each other, and the irradiation light contains a high intensity part and a low intensity part, the low intensity part being caused by the electrode, where the high intensity part and the low intensity part are alternating in a parallel manner due to the parallel arrangement of the plurality of electric conductor lines, the light emitting diode is disposed such that a longitudinal direction of the plurality of electric conductor lines arranged in parallel to each other is parallel to the direction of the long side of the rectangular opening shape of the mask member, and, thereby, such that the longitudinal direction of of the plurality of electric conductor lines arranged in parallel to each other is perpendicular to the flow direction of the flow channel, and the irradiation light passed through the through-hole is irradiated on the irradiation segment in the flow channel such that the flow of the sample solution comprising the particles in the flow channel of the flow cell is passing alternatingly through the high intensity part and the low intensity part of the irradiation light irradiated on the irradiation segment.