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 distinct 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 distinct feature amounts; a change information acquisition unit that acquires information about a change in the distinct feature amounts 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 distinct 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 a result of comparing the at least two distinct feature amounts within each of the plurality of regions between each other.