A grain oriented electrical steel sheet having a glass coating film formed on a surface thereof, comprising: a linearly altered portion generated in the glass coating film at one of side edges of the steel sheet, in a continuous line or in a discontinuous broken line in a direction parallel with the rolling direction of the steel sheet, wherein the linearly altered portion is generated only in the glass coating film and not in the base metal iron portion of the steel sheet, wherein the glass coating film comprises Mg, and wherein the linearly altered portion of the glass coating film has a composition different from that of the other portions of the glass coating film; wherein an average value R of deviation angles θa of crystal grains positioned below the linearly altered portion in a base metal iron portion of the steel sheet is 0° or more and 20° or less, when the deviation angle θa is defined as a deviation angle of a direction of an axis of easy magnetization of each crystal grain relative to the rolling direction, wherein a characteristic X-ray intensity Ia of Mg in the linearly altered portion of the glass coating film is smaller than an average value Ip of the characteristic X-ray intensity of Mg in the other portions of the glass coating film, and wherein the characteristic X-ray intensity Ia of Mg in the linearly altered portion and the average value Ip of the characteristic X-ray intensity of Mg in the other portions of the glass coating film are obtained through an Electron Probe Micro Analysis EPMA, and the linearly altered portion is identified in the glass coating film as an Mg reduced portion whose Mg reduction ratio Ir is defined as Ia/Ip and is within the range 0.3 ≤ Ir ≤ 0.95. a linearly altered portion generated in the glass coating film at one of side edges of the steel sheet, in a continuous line or in a discontinuous broken line in a direction parallel with the rolling direction of the steel sheet, wherein the linearly altered portion is generated only in the glass coating film and not in the base metal iron portion of the steel sheet, wherein the glass coating film comprises Mg, and wherein the linearly altered portion of the glass coating film has a composition different from that of the other portions of the glass coating film; wherein an average value R of deviation angles θa of crystal grains positioned below the linearly altered portion in a base metal iron portion of the steel sheet is 0° or more and 20° or less, when the deviation angle θa is defined as a deviation angle of a direction of an axis of easy magnetization of each crystal grain relative to the rolling direction, wherein a characteristic X-ray intensity Ia of Mg in the linearly altered portion of the glass coating film is smaller than an average value Ip of the characteristic X-ray intensity of Mg in the other portions of the glass coating film, and wherein the characteristic X-ray intensity Ia of Mg in the linearly altered portion and the average value Ip of the characteristic X-ray intensity of Mg in the other portions of the glass coating film are obtained through an Electron Probe Micro Analysis EPMA, and the linearly altered portion is identified in the glass coating film as an Mg reduced portion whose Mg reduction ratio Ir is defined as Ia/Ip and is within the range 0.3 ≤ Ir ≤ 0.95.