Carole Ghosn wrote in a nine-page letter Monday her husband's case highlights a "draconian system."
Ghosn, arrested Nov. 19, has been charged with underreporting income and breach of trust.
The letter describes conditions that are routine for suspects in Japan, which have come under fire from international human rights groups. It also defended Ghosn's character and record in the auto industry.
Last week, he asserted his innocence in a Tokyo court, his first public appearance since his arrest.
No trial date has been set, and he could be detained for months. Tokyo prosecutors say he is a flight risk and may tamper evidence.