iPhone: Apple Pay works with iPhone 6 and later in stores, apps and websites in Safari
Apple Watch: in stores and apps (requires iPhone 6 or later)
iPad: iPad Pro, iPad (5th generation), iPad Air 2, and iPad mini 3 and later in apps and websites in Safari
Mac: Mac (2012 or later) in Safari with an Apple Pay–enabled iPhone or Apple Watch.
You can find the full list of Apple Pay compatible devices here.