Provided is a therapeutic agent having excellent effect for influenza virus infection, comprising an active component obtained from natural substance.The therapeutic agent comprises a β-glucan containing composition obtained from the microbial culture of Aureobasidium sp. This therapeutic agent can inhibit the aggravation of influenza virus infection and promote the healing of influenza virus infection.本發明提供利用源自天然物之有效成分之流感病毒感染症的治療劑,具有優越效果者。該治療劑含有從屬於短梗黴屬微生物培養物獲得之含有β-葡聚糖之組成物作為流感病毒感染症治劑之有效成分。經由該治療劑,可抑制流感病毒感染症重症化,促進治癒。由於本案的圖為試驗例數據之圖表,並非本案的代表圖。故本案無指定代表圖。