A transformer connection phase determination device includes a processor that executes a process. The process includes: acquiring a power value consumed by at least one consumer connected to a transformer that is connected to a phase corresponding to a combination of two of plural distribution lines, and acquiring respective current values flowing in the plural distribution lines; computing a frequency component of the power value or of a current value caused by the power value, and a frequency component of the respective current values flowing in the plural distribution lines; and computing respective correlation values indicating a correlation between the power value or the current value caused by the power value and the respective current values flowing in the plural distribution lines, using each of the computed frequency components, and determining the phase to which the transformer is connected based on the respective correlation values.