Question on Mage Slayer

[rikimaru75]

Coming back from the Alara Reborn prerelease, I came across the following card:

Mage Slayer - 1RG
Artifact - Equipment   Uncommon
Whenever equipped creature attacks, it deals damage equal to its power to defending player.
Equip 3
"When the wielder is strong enough, any sword will do."
- Kresh the Bloodbraided

My question is this: Does equiped attacking creature deal its damage when chosen as a attacker with this as well as combat damage?  Or does this basically give it something like Thorn Elemental's ability but instead does not give the 'may' option that Thorn Elemental provides?

[RJ]

This equipment has a triggered ability that will trigger and then resolve when the equipped creature is declared an attacker and all costs are paid if there are any.  Combat damage will be dealt with as normal when the time comes up in the combat phase. 

[Wagner]

It says exactly what is written. When it attacks, before blockers are chosen and before any damage is done, it triggers and will do it's power in damage.

After that, the attack phases continues like always, defending players blocks etc.

Edit: Got beat to it.