Equal pay for equal work?

It's quite common on the Seoul subway to see little card-sized advertisements tucked into the frames the big ads go in.
This is a "Help Wanted" ad for what looks like a routine office admin job. I'm curious about the explicitly different salaries for men and women. This ad says they'll pay 2,000,000 won/month to men and 1,300,000 won/month to women. I know this country is widely considered to be far less committed to the ideals of sexual equality than most Western countries, but still I'm suprised at the sheer directness of this ad. They don't even try to claim they want men and women for different jobs. They want men or women for the same job, but they'll pay men a lot more. Am I misunderstanding something here? Or is there some cultural issue I don't know about?

Again, I'm cynical enough I'm not shocked that they'd pay men more - I'm just shocked that they'd be so upfront about it.