Rep. Michael E. Capuano is not officially kicking off his Massachusetts Senate bid until Friday, but that didn’t stop the six-term Boston Democrat from launching his TV advertising campaign.

Capuano began airing an introductory spot statewide on Thursday. The ad touts his ability to carry on the legacy of Democratic Sen. Edward M. Kennedy, the longtime incumbent whose death Aug. 25 created the vacancy.

“Only one candidate stood with Ted Kennedy against Bush’s Iraq War and mirrors his progressive record,” the ad begins, before reeling off a list of policies the mostly liberal Capuano supports, including a strong public health care option, abortion rights and gay marriage equality.

Capuano spokeswoman Alison Mills said the ad buy was “substantial.”