Aggreko chief financial officer Carole Cran has tendered her resignation from the group to enable her to take up a new role as CFO of Forth Ports.
Cran has been with Aggreko for 13 years including three as CFO.
Aggreko said the board would be initiating a process to identify her successor and she would leave the business following an orderly handover within the next 12 months.
Chief executive Chris Weston said: "I want to thank Carole for her support to me personally and for her outstanding dedication to Aggreko over many years. We wish her all the very best."