In the holiday snap, Gwen, 44, smiles at the camera while cradling Apollo as he feeds. She captioned the picture: 'Switzerland!!!!' followed by a baby bottle emoticon.
The photo has received more than 40,000 likes and hundreds of comments praising Gwen for breastfeeding in public.
"I love you even more for this picture! #breastfeeding #proud," wrote Instagram user madamerebecca.
"Yay for breastfeeding picture! Amazing mama! Hope you're enjoying your time in Switzerland!" wrote user coclettey.
Gwen is thought to be visiting Switzerland on a family holiday with her husband Gavin Rossdale and their three sons, Kingston, eight, Zuma, six, and baby Apollo.
On Thursday, July 24, the family were seen making their way to London Heathrow Airport, following a stay at their London home in Primrose Hill.
Gwen previously spoke about how much she enjoys breastfeeding, after she was snapped breastfeeding Zuma in a Los Angeles park when he was three months old.
Speaking about how Zuma weaned himself off breast milk on his own, she told USA Today:
"I didn't want him to [quit]. It felt like a total rejection. It was really hormonal."
"I encourage women to do it – it's just so good for the baby and good for yourself," she said.
More on Parentdish
More:Baby's First Year
Suggested For You
SUBSCRIBE AND FOLLOW
Get top stories and blog posts emailed to me each day. Newsletters may offer personalized content or advertisements.Learn more