A method of manufacturing a hot-pressed part, comprising: heating, as a blank sheet, a steel sheet to a temperature range of Ac 3 point or more and 1000 °C or less, the steel sheet including: a chemical composition containing, in mass%, C: 0.180 % or more and less than 0.300 %, Mn: 3.50 % or more and less than 11.0 %, Si: 0.01 % to 1.5 %, P: 0.05 % or less, S: 0.05 % or less, Al: 0.005 % to 0.1 %, and N: 0.01 % or less, optionally one or more groups selected from A group: one or more selected from Ni: 0.01 % to 5.0 %, Cu: 0.01 % to 5.0 %, Cr: 0.01 % to 5.0 %, and Mo: 0.01 % to 3.0 %, B group: one or more selected from Ti: 0.005 % to 3.0 %, Nb: 0.005 % to 3.0 %, V: 0.005 % to 3.0 %, and W: 0.005 % to 3.0 %, C group: one or more selected from REM: 0.0005 % to 0.01 %, Ca: 0.0005 % to 0.01 %, and Mg: 0.0005 % to 0.01 %, D group: Sb: 0.002 % to 0.03 %, and E group: B: 0.0005 % to 0.05 %, and with a balance consisting of Fe and inevitable impurities; and a microstructure that includes ferrite and cementite and in which Mnθ/Mnα is 1.4 or more, where Mnα is a Mn concentration of the ferrite and Mnθ is a Mn concentration of the cementite; retaining the steel sheet in the temperature range for 10 sec or more and 900 sec or less; and thereafter performing press forming and hardening simultaneously on the steel sheet using a tool for press forming, to obtain a hot-pressed part including a microstructure that consists of martensite of 70.0 % or more in volume fraction and retained austenite of 3.0 % or more and 30.0 % or less in volume fraction and a residual microstructure consisting of bainite, ferrite, cementite, and/or pearlite of 10 % or less in volume fraction, and in which the number of retained austenite grains of 0.3 μm or more in equivalent circular diameter is 2.0 × 10 5 /mm 2 or more. heating, as a blank sheet, a steel sheet to a temperature range of Ac 3 point or more and 1000 °C or less, the steel sheet including: a chemical composition containing, in mass%, C: 0.180 % or more and less than 0.300 %, Mn: 3.50 % or more and less than 11.0 %, Si: 0.01 % to 1.5 %, P: 0.05 % or less, S: 0.05 % or less, Al: 0.005 % to 0.1 %, and N: 0.01 % or less, C: 0.180 % or more and less than 0.300 %, Mn: 3.50 % or more and less than 11.0 %, Si: 0.01 % to 1.5 %, P: 0.05 % or less, S: 0.05 % or less, Al: 0.005 % to 0.1 %, and N: 0.01 % or less, optionally one or more groups selected from A group: one or more selected from Ni: 0.01 % to 5.0 %, Cu: 0.01 % to 5.0 %, Cr: 0.01 % to 5.0 %, and Mo: 0.01 % to 3.0 %, B group: one or more selected from Ti: 0.005 % to 3.0 %, Nb: 0.005 % to 3.0 %, V: 0.005 % to 3.0 %, and W: 0.005 % to 3.0 %, C group: one or more selected from REM: 0.0005 % to 0.01 %, Ca: 0.0005 % to 0.01 %, and Mg: 0.0005 % to 0.01 %, D group: Sb: 0.002 % to 0.03 %, and E group: B: 0.0005 % to 0.05 %, and A group: one or more selected from Ni: 0.01 % to 5.0 %, Cu: 0.01 % to 5.0 %, Cr: 0.01 % to 5.0 %, and Mo: 0.01 % to 3.0 %, B group: one or more selected from Ti: 0.005 % to 3.0 %, Nb: 0.005 % to 3.0 %, V: 0.005 % to 3.0 %, and W: 0.005 % to 3.0 %, C group: one or more selected from REM: 0.0005 % to 0.01 %, Ca: 0.0005 % to 0.01 %, and Mg: 0.0005 % to 0.01 %, D group: Sb: 0.002 % to 0.03 %, and E group: B: 0.0005 % to 0.05 %, and with a balance consisting of Fe and inevitable impurities; and a microstructure that includes ferrite and cementite and in which Mnθ/Mnα is 1.4 or more, where Mnα is a Mn concentration of the ferrite and Mnθ is a Mn concentration of the cementite; retaining the steel sheet in the temperature range for 10 sec or more and 900 sec or less; and thereafter performing press forming and hardening simultaneously on the steel sheet using a tool for press forming, to obtain a hot-pressed part including a microstructure that consists of martensite of 70.0 % or more in volume fraction and retained austenite of 3.0 % or more and 30.0 % or less in volume fraction and a residual microstructure consisting of bainite, ferrite, cementite, and/or pearlite of 10 % or less in volume fraction, and in which the number of retained austenite grains of 0.3 μm or more in equivalent circular diameter is 2.0 × 10 5 /mm 2 or more.