PROBLEM TO BE SOLVED: To provide an antidepressant which achieves high therapeutic effect in a shorter period and can be safely used without any adverse effect.SOLUTION: The pharmaceutical composition for treating/preventing depression includes an earthworm dry powder as an active ingredient. For treating/preventing depression, the pharmaceutical composition can be used alone or used in combination with one or more antidepressants selected from the group consisting of clomipramine, nortriptyline, amitriptyline, amoxapine, imipramine, trimipramine, lofepramine, dosulepin, mianserin, maprotiline, setiptiline, trazodone, paroxetine, sertraline, fluvoxamine, fluoxetine, citalopram, escitalopram, milnacipran, duloxetine, venlafaxine, nefazodone and mirtazapine.
