The Lost & Found office is ironically, quite hard to find, as it is actually outside the station building. On the north side of the station, head east, past Hotel Granvia and Kyoto Theater and keep going. Signs for the Lost & Found office will lead you to an alleyway that leads to some bicycle parking lots. The Lost & Found office is just before those parking lots.
Open: 8:00 – 19:30
There is also a Lost & Found counter specifically for shinkansen passengers in the Information office on the south side of the station.