Voting in the country of over five million people began at 0700 local time and will continue until polling stations close at 1900 local time, the central electoral commission confirmed.
Berdymukhamedov, 59, faces eight other candidates including subordinate regional officials, the director of a government-owned oil refinery and a representative of the Central Asian country's state agribusiness complex.
But these other men are viewed as token opponents for the former dentist and health minister who rose to power suddenly following the shock death of predecessor Saparmurat Niyazov in 2006.
"I do not know on what merits or for what reasons the others became candidates. Therefore, I will vote for Berdymukhamedov," she said.
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Recent footage from state television saw Berdymukhamedov in relaxed form during a low key pre-election campaign.
One of his public appearances showed him decked in casual attire as he impressed factory workers by strumming along on the guitar to a song state media claims he wrote himself.
The grand pledge at the centre of his campaign is to "ensure the prosperity of independent, neutral Turkmenistan in the third millennium".
The ballot in Turkmenistan comes after Berdymukhamedov signed off on constitutional changes that analysts saw as removing barriers to his lifelong rule.
That fix extended presidential terms from five to seven years and abandoned the upper age limit for candidates.
"These regimes have a logic of their own and they very much follow that logic," said Annette Bohr, an associate fellow of the Russia and Eurasia programme at Chatham House think tank.
If anything, Bohr said, Turkmenistan's regime is "even more repressive and personalist" than those found in neighbouring Kazakhstan and Uzbekistan.
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