A modified conjugated diene polymer satisfying the following conditions (I) to (IV): (I) at least two peaks are observed in a molecular weight distribution curve; (II) when a peak of the highest molecular weight is defined as a peak (B), a peak of the largest peak area except for the peak (B) is defined as a peak (T), a peak molecular weight of the peak (B) is from 500,000 to 2,500,000 and a peak molecular weight of the peak (T) is from 150,000 to 600,000; (III) an area of the peak (T) is from 30% to 80% and a total value of an area of the peak (B) and the area of the peak (T) is 65% or more; and (IV) a proportion of a modified polymer chain(s) in a region ranging from a low-molecular-weight side to a point of 5% cumulative area is from 60% to 99%.