He adopted a habit of giving card slots a wiggle before putting his card in.
"I do a good enough job emptying out my account on my own, I don't need someone else doing it for me," he joked.
He posted pictures of his find on Facebook.
"I thought everyone needs to know what one of these things looks like, and that they can remove them."
Kiwibank communications manager Bruce Thompson said the company was grateful the customer got in touch so quickly.
"The police have been contacted and we are waiting for them to uplift the skimming device," he said.
"As always, we will protect customer's accounts from fraudulent activity."
He would not say how long the device might have been on the machine or how many customers could be impacted.
"Kiwibank is working closely with the police on this issue. With a criminal investigation under way, we don't wish to provide a lot of details about the event," Mr Thompson said.
Kiwibank ATMs in Tauranga were among those targeted by a suspected skimming gang in April.
At least two dozen people had their bank cards compromised. Three people lost more than $1000 after their cards were cloned and used around Brookfield.
Police could not comment on the case, yesterday.
How to spot a card skimmer and protect yourself
- Before you use an ATM, look for inconsistencies in colours, materials, or graphics - Check the top of the ATM, speakers, side of the screen, card reader and keyboard for evidence of tampering - If anything does not look right, do not use the machine - Note where and when you use your card - Cover your pin when completing a transaction.
If you think you've been skimmed, check your account and contact your bank to close your account as soon as possible. Report it to the police.