Hemubhai Makwana, 38, and his wife Hansaben, 35, set up the device so that their severed heads would roll into a fire altar, Indian cops say.
Authorities said the pair left a suicide note for their son and daughter, parents and relatives.
Police added that they had killed themselves at their home in Gujarat on Sunday so they could offer their heads for a sacrificial ritual.
Vinchhiya police sub-inspector Indrajeetsinh Jadeja said the couple used a “guillotine-like mechanism”.
He added: “We are recording statements of the family members and trying to know the reason behind the couple’s extreme step.”
The note found by cops urged their relatives living nearby to take care of their parents and children.
Jadeja said the day before the incident, the parents had sent their two kids to their uncle’s house, reports Times of India.
Hemubhai and Hansaben’s bodies were sent for a post-mortem.
A case of accidental death has been registered.
According to the pair’s relatives, they had been offering prayers in a hut every night since last year.
In some parts of India black magic is still practised.
Last year, a couple were accused of murdering two women before eating their flesh.
Bhagaval and Laila Singh allegedly chopped up their two victims and cooked them as part of a sick ritual they believed would “preserve their youth”.
The pair, from Kerala and another man named Rasheed alias Muhammand Shafi – who allegedly masterminded the killings – have been arrested.
According to cops, the trio “sacrificed” two women, both in their 50s, “in the name of superstition and black magic”.
The couple also believed killing the women would help better their financial situation, it is reported.
Some evil religion gave them French Royalty Syndrome…