A very big PPK...
The holster is for a Browning Hi Power, "Pistole 640b" as Ade pointed out few years ago? ;-) It's an instantly recognizable holster on account of very tall mag pocket, otherwise looks much like a P38 "breakaway" holster.
The Hi Power was the only pistol of this time to have a "double stack" mag, holding 13 rounds if I remember correctly, so the mag is twice as fat as a P38 mag, hence the cavernous mag pocket.
The Hi Power holds the distinction of being [virtually] the only pistol used by both side during the war, with the minor exception of the Norwegian Mod 1914 which is basically a Colt 1911, another older John M. Browning design, but a waffen proofed M1914 +Pistole 657n" would be a pretty scarce pistol to get your hands on.
During the German occupation of Norway (1940–1945), manufacture of the pistol, given the designation Pistole 657(n), was continued under German control. The Waffenamt acceptance mark (WaA84) was added in 1945 and only those 920 pistols produced that year were ever Waffenamt-marked. It's not likely that any of these Waffenamt-marked pistols ever saw any action during World War II as the first one, serial# 29615, was delivered March 29, 1945 and the last one, serial# 30534, was delivered on 5 May 1945 just before liberation of Norway. In total, approximately 8200 pistols were made during German occupation (serials 22312-30534). All of them were delivered to AOK Norwegen (Army) except 700 that were delivered to Maza Norwegen (Navy).
1940 = approx. 50 pistols
1941 = approx. 4099 pistols
1942 = 3154 pistols
1945 = 920 pistols
No pistols were produced in 1943 & 1944. In those years, production of Krag-Jørgensen rifles was prioritized.
The Hi Power was much used by the Germans, as they took over the FN plant in 1940 (interesting factoid, if I remember right, they had also taken over this same plant back in WWI?). The early pistols had tangent sights and are very desirable. The Hi Power was supposedly well like and maybe even issued to Fallschrimjager, and also SS troops? It was after all a Hi Capacity pistol, the P.08 Luger only held 7 (+1) rounds, the P38 and 1911 8 (+1) rds.
As the Germans took over the FN plant, plans were smuggled out and the Hi Power was made by Inglis in Canada, many tangent sighted. These made their way into the hands of elite (Commando) British troops. Inglis also made these for the Chinese during the same time period.
Post war, the pistol was adopted by 40 some countries around the world.
A truly iconic pistol.
PS Anyone feel free to correct any misinformation on my part, I'm drawing most of the Hi Power info from things I picked up along the way, most before the internet existed.