Its a breech loader, most likely a 22 though I have seen other calibers in rifles using the same action. Pull the hammer back then pivot the simple breech open to load. A variation of the Flobert action iirc. Have seen these referred to as "parlor pistols" made for indoor practice using 22CB or BB caps. While not common they are not particularly valuable. All the ones I've run across had Belgian proofs.

That one appears to have a badly split stock and I see the trigger guard is separate in the second pic. Probably repairable but unless the bore is in good shape fit only for decorator use. If the bore is decent and it is a 22 DO NOT use modern high speed 22 ammo in it. The action isn't strong enough for regular use of modern rounds. Low powered CB or BB loads only.