A method for manufacturing a high-strength and high-toughness thin steel by heat-treating a steel raw material, comprising: using a thin low-carbon steel having a thickness of 1.2 mm or less as the steel raw material which is a reception material of heat treatment; a first process of rapidly cooling the thin low-carbon steel after rapid heating thereof to obtain a martensite structure; and a second process of rapidly cooling the thin low-carbon steel which have been subjected to the first process after rapidly reheating the same to a temperature lower than a temperature at a rapid heating time in the first process, wherein the first process and the second process are implemented while the thin low-carbon steel is being relatively moved to each heating section and each cooling section which perform rapid heating and rapid cooling treatments in the first process and the second process; the first process includes a step of rapidly heating the thin low-carbon steel up to a temperature of 1000°C or higher at a rate of 300°C/second or more and a step of rapidly cooling the thin low-carbon steel at a rate of 300°C/second or more after the thin low-carbon steel is held at a temperature of 900°C or higher within ten seconds; and the second process includes a step of rapidly heating the thin low-carbon steel up to a temperature of 700°C or higher at a rate of 300°C/second or more after the cooling in the first process and a step of rapidly cooling the thin low-carbon steel at a rate of 300°C/second or more after the thin low-carbon steel is held at a temperature of 600°C or higher within ten seconds, wherein a heat treatment apparatus which treats the thin low-carbon steel is provided with a first heating section which performs the rapid heating treatment in the first process, a first cooling section which performs the rapid cooling treatment in the first process, a second heating section which performs the rapid heating treatment in the second process, and a second cooling section which performs the rapid cooling treatment in the second process, and the thin low-carbon steel is sequentially treated in the first heating section, the first cooling section, the second heating section, and the second cooling section, wherein the first heating section and the second heating section are composed of one heating section having a predetermined length extending in a moving direction, and the cooling treatment in the first process and the cooling treatment in the second process can be performed to the thin low-carbon steel which is a target to be treated from opposite faces thereof. using a thin low-carbon steel having a thickness of 1.2 mm or less as the steel raw material which is a reception material of heat treatment; a first process of rapidly cooling the thin low-carbon steel after rapid heating thereof to obtain a martensite structure; and a second process of rapidly cooling the thin low-carbon steel which have been subjected to the first process after rapidly reheating the same to a temperature lower than a temperature at a rapid heating time in the first process, wherein the first process and the second process are implemented while the thin low-carbon steel is being relatively moved to each heating section and each cooling section which perform rapid heating and rapid cooling treatments in the first process and the second process; the first process includes a step of rapidly heating the thin low-carbon steel up to a temperature of 1000°C or higher at a rate of 300°C/second or more and a step of rapidly cooling the thin low-carbon steel at a rate of 300°C/second or more after the thin low-carbon steel is held at a temperature of 900°C or higher within ten seconds; and the second process includes a step of rapidly heating the thin low-carbon steel up to a temperature of 700°C or higher at a rate of 300°C/second or more after the cooling in the first process and a step of rapidly cooling the thin low-carbon steel at a rate of 300°C/second or more after the thin low-carbon steel is held at a temperature of 600°C or higher within ten seconds, wherein a heat treatment apparatus which treats the thin low-carbon steel is provided with a first heating section which performs the rapid heating treatment in the first process, a first cooling section which performs the rapid cooling treatment in the first process, a second heating section which performs the rapid heating treatment in the second process, and a second cooling section which performs the rapid cooling treatment in the second process, and the thin low-carbon steel is sequentially treated in the first heating section, the first cooling section, the second heating section, and the second cooling section, wherein the first heating section and the second heating section are composed of one heating section having a predetermined length extending in a moving direction, and the cooling treatment in the first process and the cooling treatment in the second process can be performed to the thin low-carbon steel which is a target to be treated from opposite faces thereof.