k-fed needs the pop tart to pay up.

this really shouldn't come as a surprise. kevin federline is broke. his average annual income is about $20,000. his legal fees - eight times that.

so now the single father of four is asking britney to pay his legal fees. and a judge has obliged, ordering unfitney to pony up $120,000 for k-fed and his lawyer, mark vincent kaplan.

tmz obtained all of the unshocking documents, which you can read here.