Currently in Japan, discontinuing an invasive mechanical ventilator (IMV) is illegal; therefore IMV-related decision making is a crucial issue. This study examined IMV decision-making factors and psychological conflict in 50 patients with amyotrophic lateral sclerosis. The Herth Hope Index was used for the assessment of pre- and post-IMV conflict. Interviews identified some decision-making factors: patient's decision, patient's and family's mutual decision, family's decision, and emergency-induced without patient's or family's consent. Participants who experienced no IMV-related regret received sufficient prior IMV education from physicians and nurses, and time for reflection and family consultation. Their hope was similar to their pre-onset levels. Patients who received no prior IMV education accepted treatment as a natural progression. Their hope levels were lower than pre-onset. Those who received only a brief prior IMV explanation rejected the ventilator, experiencing regret if they were given an emergency IMV. Their hope levels were among the lowest. However, some of these patients managed to overcome their regret through being helped by nurses. Sufficient physician explanation and nursing advocacy for autonomous patient decision making are critical for improving hope in this patient group.