That is a Multi Amp tester to check relays and circuit breakers. This "machine" will put put variable amperage across a breaker to test for operation along with how long the breaker takes to trip……. Notice the "stop clock" on the upper panel. I have used a multi amp machine (similar to this) to test over loads on starters, high voltage relays, circuit breakers.
Back in the late 1970’s I spent 8 weeks at the multi amp headquarters in Duncanville, Texas learning how to use their test equipment and calibrating high voltage relays.
This machine that the OP posted is a medium sized machine…… I have used some multi amp machines that are the size of two refrigerators and weigh 800 pounds.
BTW! The value of this ANTIQUE machine in the pics is worthless scrap and it would be almost impossible to find any one to buy it even for parts.