To provide a technique for adsorbing heavy metals in a capsule by a heavy metal adsorbent in a capsule without using an adsorbent.

A heavy metal adsorbent is sealed in a capsule insoluble in a heavy metal-containing solution and permitting heavy metal ions to be removed to pass to make heavy metals adsorbed in the capsule. This method can be utilized in the small-scale treatment of a heavy metal-containing waste liquid.