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 includes: a supply device for supplying a medicinal agent of interest to a container capable of being filled with the medicinal agent a conveyance device for conveying the container and a detecting unit for obtaining measurement data corresponding to an outer diameter of the container in a conveyance direction of the container by the conveyance device. Based on the measurement data, the conveyance device stops the container at a supply position where the medicinal agent can be supplied from the supply device to the container.
