Justin Baldoni's leaning on his loved ones in the middle of his extensive legal battle with Blake Lively ... saying he's relying on his friends and family to help him through.

Photogs caught up with the actor early Friday morning walking into LAX ... and, they simply asked how he's holding up during this difficult time.

Baldoni -- who's holding hands with one of his kids in the clip and walking with his wife, Emily -- says he's grateful to be with his family while he and Blake trade legal filings.

Justin says his family is one of the most important tentpoles he's leaning on right now ... right up there with his close friends and his faith.

This is Baldoni's first appearance out since he filed a $400 million lawsuit against Lively, her husband Ryan Reynolds, and public relations pro Leslie Sloane.

He's suing them for defamation, civil extortion, and a slew of other allegations ... and claims they participated in an alleged smear campaign against him, after Blake accused him of sexual harassment and engaging in a coordinated effort to destroy her reputation. He's also suing the New York Times for $250 million for defamation.

Lively's team fired back at Justin's lawsuit ... claiming Justin's just trying to shift the narrative to place blame on Blake -- who is actually the victim here.

They add, "In short, while the victim focuses on the abuse, the abuser focuses on the victim. The strategy of attacking the woman is desperate, it does not refute the evidence in Ms. Lively’s complaint, and it will fail."