There is provided a medicinal agent filling device with reduced size, which can automatically fill a medicinal agent into containers having different sizes. A medicinal agent filling device (1) includes: a supply device (10) for supplying a medicinal agent (M) of interest to a container (26) capable of being filled with the medicinal agent (M) a conveyance device (30) for conveying the container (26) and a detecting unit for obtaining measurement data corresponding to an outer diameter (d) of the container (26) in a conveyance direction of the container (26) by the conveyance device (30). Based on the measurement data, the conveyance device (30) stops the container (26) at a supply position (L) where the medicinal agent (M) can be supplied from the supply device (10) to the container (26).
