In a modified conjugated diene-based polymer, a ratio of a coupling polymer, obtained by gel permeation chromatography (GPC), is 70% by mass or more based on a total amount of the modified conjugated diene-based polymer, and a modification ratio obtained by adsorption GPC is 70% by mass or more based on a total amount of the modified conjugated diene-based polymer, and when Mooney viscosity ML1+4 (100° C.) measured at 100° C. is represented by ML and a weight average molecular weight obtained by GPC is represented by Mw, ML≤1.8 (Mw×10−4)−31.5, and Mooney viscosity ML1+4 (100° C.) measured at 100° C. is 30 to 150.