To provide a rent calculation system for work machine capable of calculating a reasonable rent, reducing the time and labor of rent calculation work for a lender and accelerating the utilization of work machine by a borrower.

The rent calculation system for work machine calculating the rent of work machines 1 and 2 is provided with an operation information acquisition means 25 acquiring operation information of the work machines 1 and 2 lent to the borrower, a standard operation time acquisition means 28 acquiring standard operation time during a preset lending period corresponding to the lent work machines 1 and 2, a standard rent acquisition means 29 acquiring a standard rent corresponding to the acquired standard operation time, a basic rent acquisition means 30 acquiring a basic rent corresponding to basic operation time which is about a half of the standard operation time and a rent setting means 31 setting either the standard rent or the basic rent as the rent for the borrower based on the calculated accumulated real operation time.