A method of writing a content through a writing input on a touch screen, the method comprising: detecting a writing input; displaying written input content corresponding to the detected writing input; and identifying whether a proofreading mode is set; wherein if the proofreading mode is set, the method further comprises: entering a proofreading mode; detecting an input of one of a plurality of preset proofreading marks (601, 701, 801, 1101) in the written input content; and applying a content editing function to the written input preset for the corresponding proofreading mark (601, 701, 801, 1101); characterized in that the plurality of proofreading marks includes a slope proofreading mark indicating proofreading of a slope of a part corresponding to a character string including a plurality of characters in the written content; and wherein, in a proofreading operation according to the slope proofreading mark, a form connecting the character string including the plurality of characters in the written content by one line is recognized as the slope proofreading mark and the characters are moved and rotated based on a stroke of the recognized slope proof reading mark as a guideline either in a direction making slopes of the characters become zero degrees or in a direction matching slopes of the characters with an approximate slope of the guideline. detecting a writing input; displaying written input content corresponding to the detected writing input; and identifying whether a proofreading mode is set; wherein if the proofreading mode is set, the method further comprises: entering a proofreading mode; detecting an input of one of a plurality of preset proofreading marks (601, 701, 801, 1101) in the written input content; and applying a content editing function to the written input preset for the corresponding proofreading mark (601, 701, 801, 1101); characterized in that the plurality of proofreading marks includes a slope proofreading mark indicating proofreading of a slope of a part corresponding to a character string including a plurality of characters in the written content; and wherein, in a proofreading operation according to the slope proofreading mark, a form connecting the character string including the plurality of characters in the written content by one line is recognized as the slope proofreading mark and the characters are moved and rotated based on a stroke of the recognized slope proof reading mark as a guideline either in a direction making slopes of the characters become zero degrees or in a direction matching slopes of the characters with an approximate slope of the guideline. entering a proofreading mode; detecting an input of one of a plurality of preset proofreading marks (601, 701, 801, 1101) in the written input content; and applying a content editing function to the written input preset for the corresponding proofreading mark (601, 701, 801, 1101); characterized in that the plurality of proofreading marks includes a slope proofreading mark indicating proofreading of a slope of a part corresponding to a character string including a plurality of characters in the written content; and wherein, in a proofreading operation according to the slope proofreading mark, a form connecting the character string including the plurality of characters in the written content by one line is recognized as the slope proofreading mark and the characters are moved and rotated based on a stroke of the recognized slope proof reading mark as a guideline either in a direction making slopes of the characters become zero degrees or in a direction matching slopes of the characters with an approximate slope of the guideline.