Howie Mandel went to his favorite Starbucks for a coffee, and left in an ambulance after passing out outside the coffee chain.

Folks who were there tell TMZ … Howie was at his local Starbucks in Woodland Hills with his wife and friends Wednesday when he suddenly passed out, falling over and then being laid out on a cement bench.

We’re told paramedics were called to the scene and the “America’s Got Talent” judge was rushed to a hospital in Tarzana.

It looks like Howie was able to sit up by the time the Los Angeles Fire Department arrived … but it was definitely a scary situation.

We’re told customers who were there knew him and were shocked to see it all go down.

Sources close to Howie tell us he frequents this particular Starbucks … and we’re told they think he fainted from low blood sugar and doctors are now running tests at the hospital.

Story developing …