The robbery took place in Rinkeby, a suburb to the north-west of the city centre, at around 9am. The robbers were armed with a pistol and an axe, according to reports.
One of the guards was hit during the attack, but did not need hospital treatment, according to Towe Hägg, spokeswoman for Stockholm Police.
It is so far unclear how much money the men have stolen.
Robberies of cash delivery vehicles have become a serious problem in Sweden during the past two years, leading to calls for steps to improve security.