The present invention provides a modified conjugated diene-based polymer having a weight-average molecular weight of 20 × 10 4 or more and 300 × 10 4 or less, in which the modified conjugated diene-based polymer having a molecular weight of 200 × 10 4 or more and 500 × 10 4 or less is comprised in an amount of 0.25% by mass or more and 30% by mass or less based on a total amount of the modified conjugated diene-based polymer, and a shrinking factor (g') is less than 0.64.