An apparatus for culturing cells using a culture medium, including: a replacer that replaces the culture medium in a culture vessel held by a holder; a measurer that measures a pH of the culture medium in the culture vessel; and an instructor that instructs the replacer to replace the culture medium in the culture vessel, wherein the instructor gives an instruction when the pH measured by the measurer is less than a predetermined pH threshold at a first replacement of the culture medium, and gives an instruction when the pH measured by the measurer is less than the predetermined pH threshold and the interval is less than an interval of a previous replacement of the culture medium at second and subsequent replacements of the culture medium.