Abstract: The purpose of the present invention is to provide a novel injectable agent having an excellent medicinal agent sustained release property. The injectable agent according to the present invention comprises a medicinal agent, trehalose and gellan gum. It is preferred that the contents of the medicinal agent, trehalose and gellan gum are 0.0001 to 50.00% (w/v), 0.1 to 50.0% (w/v) and 0.01 to 3.00% (w/v), respectively, relative to the total volume of the injectable agent. It is also preferred that the injectable agent can form a depot upon exposure to a phosphate buffer solution or a body fluid (tear fluid, vitreous fluid, etc.).