How to download all photos from Google Photos into device?

I wanted to do a factory reset. I made a backup of my device using "Setting" → "Accounts and backup" → "Google drive" → "Back up data" → "Back up now" → under "Photos and videos" I checked "Backup photos and videos from this device to your Google Account" checkbox. After one hour the backup completed. I did factory reset, chose to restore from backup and selected the backup file. Now everything got restored except the Gallery photos. Those photos appear in Google Photos. I have around 950 photos. How do I download all of them *at once*, so that they become available in my Gallery app?