1. A stem cell differentiation determination device comprising: an observation image acquisition unit that captures an image of an observation region including a stem cell in time series to acquire at least two observation images; a feature amount acquisition unit that acquires at least two feature amounts of the stem cell within a plurality of regions within the observation region for each observation image; a determination unit that determines whether or not the stem cell has been differentiated within each of the plurality of regions, on the basis of the at least two feature amount; a change information acquisition unit that acquires information about a change in the feature amount within each of the plurality of regions between the observation images captured in time series or information about a change in a determination result from undifferentiation to differentiation within each of the plurality of regions between the observation images; an output unit that outputs the information about a change in the feature amounts within each of the plurality of regions or the information about a change in the determination result within each of the plurality of regions; and a reliability acquisition unit that acquires a degree of reliability for the determination results for each of the plurality of regions, based on the at least two feature amounts within each of the plurality of regions.