Richard Burton, 49, of Barton Cottages, Huntsham, near Tiverton in Devon, denied six charges of indecent assault.
He was found guilty of four of the offences by Exeter Crown Court and sentenced to three and a half years in prison.
During the week-long trial the jury heard how one of the girls developed a crush on him and was a willing partner.
The court heard a sexual relationship started when she was 14 and continued after she had turned 16 until she moved away from the area.
Of the five charges relating to this girl, Burton was found guilty of three.
A sixth charge related to Burton touching another girl's breast after taking her for a ride in his car.
Burton, who runs a business in Cullompton, told the jury he had a short sexual relationship with the first complainant, but everything was consensual as she was 17.
He denied any sexual contact with the second complainant and said the allegations had caused him a great deal of distress and were completely untrue and invented.
Nicolas Gerasimidis, defending, said Burton had lived a blameless life for 20 years and was a devoted father. He said his business would probably fold while he was in jail.
Recorder David Bartlett said: "I cannot accept you did not realise this girl was vulnerable. It must have been clear she was a troubled individual and there was a disparity of age between you.
"I have no doubt she was infatuated with you and a willing participant but you were 17 years older and should have exercised self-restraint to resist her obvious sexual drive until she was at least 16."
A businessman has been jailed for sexually abusing two schoolgirls more than 20 years ago.