Repairman

A  is a special type of Blacksmith that specializes in Equipment repair. Weapons and armor that has been damaged in battle can be repaired by a. Destroyed equipment, such as that destroyed by refinement failure, cannot be repaired.

Ragnarok Online
Repairmen in RO will only repair equipment that is currently equipped and costs 5,000 Zeny per piece of broken equipment.

Ragnarok Online II
Since equipment durability degrades with use, it needs to be repaired regularly by talking to a nearby repairman and choosing [Repair] or [Repair All] options to repair your equipment. Repair costs scale with the amount of durability lost. The general formula per piece of equipment is:

"Durability value lost x 2 Rupi"

NPCs can be found in all towns and cities. Simply look for the hammer icon on your minimap to locate them.