A cash sum of £3 million will be paid on completion with up to £2.6 million payable depending on AMP's financial performance in the two years to May 2008.
AMP has a fleet of 525 powered access machines across four depots in the south west.
The deal follows the acquisition of Dunstable hirer Panther Work Platforms for £7 million and Bristol-based Kestrel for £4.3 million earlier this year.
Lavendon's chief executive Kevin Appleton said: 'AMP has an excellent
reputation and holds a strong position in the south west with a number of its customers showing significant growth potential.
'Following on from our earlier acquisitions of Panther and Kestrel, the complementary geographic coverage of AMP is an important addition to our new network of regional businesses.'
AMP's pre-tax profit reached £1 million in the year to August 2005 with a turnover of £4.8 million.
The firm's management team will remain with the business.