A method for producing a ceramic sintered body, comprising: heat-treating a raw material mixture containing: a first nitride containing at least one alkaline earth metal element M 1 selected from the group consisting of Ba, Sr, Ca, and Mg, a second nitride containing at least one metal element M 2 selected from the group consisting of Eu, Ce, Tb, and Mn, and a third nitride containing Si, at a temperature in a range of 1,350°C or more and 1,650°C or less in an atmosphere containing nitrogen to obtain the nitride fluorescent material having a crystallite size of 550 Å or less and a composition represented by the following formula (I): (M 1 1-y M 2 y ) 2 Si 5 N 8 (I) wherein M 1 represents at least one alkaline earth metal element selected from the group consisting of Ba, Sr, Ca, and Mg; M 2 represents at least one metal element selected from the group consisting of Eu, Ce, Tb, and Mn; and y satisfies 0.001 ≤ y < 0.5; preparing a molded body that contains the nitride fluorescent material wherein the content of nitride fluorescent material having a crystallite size of 550 Å or less in the molded body is 95% by mass or more, wherein the method for forming the molded body is a die press molding method, and a pressure at the time of die press molding is in a range of 5 MPa or more and 50 MPa or less, and calcining the molded body at a temperature in a range of 1,600°C or more and 2,200°C or less to obtain a sintered body. heat-treating a raw material mixture containing: a first nitride containing at least one alkaline earth metal element M 1 selected from the group consisting of Ba, Sr, Ca, and Mg, a second nitride containing at least one metal element M 2 selected from the group consisting of Eu, Ce, Tb, and Mn, and a third nitride containing Si, at a temperature in a range of 1,350°C or more and 1,650°C or less in an atmosphere containing nitrogen to obtain the nitride fluorescent material having a crystallite size of 550 Å or less and a composition represented by the following formula (I): (M 1 1-y M 2 y ) 2 Si 5 N 8 (I) wherein M 1 represents at least one alkaline earth metal element selected from the group consisting of Ba, Sr, Ca, and Mg; M 2 represents at least one metal element selected from the group consisting of Eu, Ce, Tb, and Mn; and y satisfies 0.001 ≤ y < 0.5; a first nitride containing at least one alkaline earth metal element M 1 selected from the group consisting of Ba, Sr, Ca, and Mg, a second nitride containing at least one metal element M 2 selected from the group consisting of Eu, Ce, Tb, and Mn, and a third nitride containing Si, at a temperature in a range of 1,350°C or more and 1,650°C or less in an atmosphere containing nitrogen to obtain the nitride fluorescent material having a crystallite size of 550 Å or less and a composition represented by the following formula (I): (M 1 1-y M 2 y ) 2 Si 5 N 8 (I) wherein M 1 represents at least one alkaline earth metal element selected from the group consisting of Ba, Sr, Ca, and Mg; M 2 represents at least one metal element selected from the group consisting of Eu, Ce, Tb, and Mn; and y satisfies 0.001 ≤ y < 0.5; M 1 represents at least one alkaline earth metal element selected from the group consisting of Ba, Sr, Ca, and Mg; M 2 represents at least one metal element selected from the group consisting of Eu, Ce, Tb, and Mn; and y satisfies 0.001 ≤ y < 0.5; preparing a molded body that contains the nitride fluorescent material wherein the content of nitride fluorescent material having a crystallite size of 550 Å or less in the molded body is 95% by mass or more, wherein the method for forming the molded body is a die press molding method, and a pressure at the time of die press molding is in a range of 5 MPa or more and 50 MPa or less, and calcining the molded body at a temperature in a range of 1,600°C or more and 2,200°C or less to obtain a sintered body. <EOS>