Objective: Leaving a portion of meals uneaten, known as plate waste, is a serious problem among children in Japan. Although children's confidence that they can completely finish meals is related to plate waste, the circumstances that influence this confidence are not known. This study examined situations in which low self-efficacy for finishing their meal occurs among elementary school children in Tokyo, Japan. Design: A survey using a cross-sectional self-reporting questionnaire was conducted in December 2009. This questionnaire included items about plate waste behaviour, self-efficacy for completely finishing meals in specific situations, sex, height and weight. Methods: A total of 2659 Japanese 5th-grade students completed the questionnaire. Univariate logistic regression and multivariate logistic regression analyses were performed with the plate waste behaviour item, the not-completely-eaten group and the completely-eaten group as dependent variables, and with the self-efficacy items as independent variables. Results: Significant correlations were found between plate waste and low self-efficacy for completely finishing meals "when portion size is too large" (boys: Odds ratio (OR) = 3.94; 95% Confidence interval (CI) = 2.83, 5.49 and girls: OR = 2.68; 95% CI = 2.03, 3.54), "when food one dislikes is served" (boys: OR = 3.74; 95% CI = 2.77, 5.04 and girls: OR = 2.89; 95% CI = 2.21, 3.76), and "when the time allowed to eat is too short" (boys: OR = 1.57; 95% CI = 1.16, 2.14 and girls: OR = 1.49; 95% CI = 1.13, 1.97). Low self-efficacy "when a meal is not delicious" (OR = 1.79; 95% CI = 1.32, 2.43) was a predictor of plate waste only among boys. Conclusions: The results suggest that in Japan environmental improvement and nutritional education are related to children's plate waste.