To provide a cleaning solution which satisfies the sure execution of cleaning a letter ring used for number printing and allowing the letter ring to hold a lubricating ingredient sufficiently, and is environment-friendly at the same time.

The cleaning solution is constituted by adding 0.1-10 vol% of a wax to an alkali solution. The cleaning solution further contains 0.1-5.0 vol% of a compatibility agent and/or a proper amount of a coloring dye. The wax is a 50-70C paraffine wax having a coefficient of viscosity of 1-10 poise (20C).