collecting maniac; obsessive collector
A person who is fanatical about collecting things; often used in a slightly humorous or self-deprecating way.
He's a stamp-collecting maniac; his room is full of stamps.
I'm an obsessive book collector, so my bookshelves fill up quickly.
Compound of 収集 (collection) and 魔 (demon, mania), literally 'collection demon'. The 魔 suffix is used to indicate an obsessive enthusiast.