Ashton Kutcher Selling House -- Dumping L.A. Mansion ... It's Not Baby Proof!

Ashton Kutcher is ditching the bachelor life ... He's put his sick Los Angeles mansion up for sale ... we're told because it isn't a good place to raise a baby.

According to our sources, Ashton pocket listed his Lake Hollywood Estates home for $12 million. He bought the place in 2012 for $8.455 MIL, snatching it up as Justin Bieber was eying it.

The home is 9,385 sq. ft. with five bedrooms and eight bathrooms. It also has a colorful history ... it was the location of one of many "swatting" pranks.

Ashton and fiancee/baby mama-to-be Mila Kunis quietly scooped up a $10.215 million home in the Beverly Hills Post Office area -- a modest 7,351 sq. ft. with three bedrooms and four baths.