A modified conjugated diene-based polymer having a weight average molecular weight of 20×104 or more and 300×104 or less, and having a molecular weight distribution Mw/Mn of 1.6 or more and 4.0 or less, wherein a modification ratio with respect to a total amount of the conjugated diene-based polymer is 50% by mass or more, a modification ratio of a component having a molecular weight which is ½ of a molecular weight at a peak top, or a peak top of the minimum molecular weight when a plurality of the peak tops of molecular weights is present, in a gel permeation chromatography curve is ½ or more of the modification ratio with respect to the total amount of the conjugated diene-based polymer, and a content of nitrogen contained in the modified conjugated diene-based polymer is 3 mass ppm or more and 70 mass ppm or less.