A very simple op amp will do this...

Current must be going to ground though.

This was posted earlier by Bill.

I don't recall you telling us what the output impedance (Zo) of your current source is. I believe the opamp gain will be R/Zo.

 

This deals with op amp theory. The impedance out will approach 0Ω very closely, it is the nature of an op amp, it tries to compensate with gain. The drive is a different issue. In many ways it resembles power supply theory, for good reason, it is where the concept of negative feedback for power supplies comes from.

Work it out, if the voltage out on the op amp drops due to loading, what will the op amp do? It is also the reason the - input is virtual ground, they are all part and parcel of the same package.

The virtual ground will be 0 ohms also (though this is an illusion). The circuit simply translates current in to voltage out, which was the original request.

If R = 1KΩ then 1ma in will create -1V out. It is extremely straightforward. Other than the power supply requirements, even a 741 would work (though I would not recommend one).

 

Until the OP reads up on op-amps, I think all he needs to know for now is that they have a variable gain, easily set by the user using feedback resistors, with a practical range of 1-100. Those numbers a wild guess on my part, but I'm quite sure they can be attained with almost every op-amp. Of course the device cannot output more voltage or current than it is supplied, and in fact input voltages near the rails can be a problem.