Yes, Apple Pay is secure. A unique Device Account Number is securely stored on a chip in the device so payment can be made without any card information having to be shared with the retailer.
Other features which help to keep your payments secure and safe include:
iPhone and iPad payments can only be authorised by using Touch ID (if it is enabled), or by entering the device passcode.
Apple Watch payments can only be authorised if the device passcode has been entered and skin contact with the device has not been lost.
Please note: you should never share your device passcode, or register more than one person’s fingerprint to Touch ID, while your card is registered to Apple Pay.