A belt drive system including an assembly of a heavy-duty drive V-belt 5 and pulleys 2 and 4 reduces noise generating owing to belt travel while ensuring the durability of the pulleys 2 and 4. The surfaces of belt grooves 6 in the V-pulleys 2 and 4 are micro-blasted or burnished so that their surface roughness satisfies the relational expression y≦−0.9×tp+100, where tp is the load length rate at a given position of a roughness curve indicating the surface features of the groove surfaces in the V-pulleys 2 and 4 and y is the variable (the degree of height) indicating by percentage the ratio of the height from the lowest valley having a maximum depth to the given position to a maximum height Ry.