Despite the increasing need for nursing care services, the turnover rate of care workers is high in Japan. Since the most common reason for quitting nursing care jobs was problems with interpersonal relationships at work, creating psychosocially safe working environments is urgent. This study aimed to investigate the mediating effects of trust in supervisors (TS) on the association between positive feedback (PF)/negative feedback (NF) and work engagement (WE) based on the job demands-resources theory and conservation of resources theory. We conducted anonymous cross-sectional surveys of 469 employees at elderly care facilities in Japan. Structural equation modeling was used to investigate the causal relationships between the variables. The results showed that PF had significant positive effects on WE, directly and indirectly through TS. By contrast, NF had a nonsignificant positive effect on TS or WE. Tucker-Lewis Index [TLI] was 0.917, Comparative Fit Index [CFI] was 0.927, Root Mean Squared Error of Approximation [RMSEA] was 0.096, and Standardized Root Mean squared Residual [SRMR] was 0.042. The study results indicate that sufficient PF is needed to improve subordinates' WE through TS in elderly care facilities.