PURPOSE: To obtain a method for detecting harmful metal capable of simply detecting whether a prescribed amount or above of harmful metal is contained in liver water, lake water, water for agriculture or industrial discharge water which is water to be detected.

CONSTITUTION: (1) This method for detecting a harmful metal is to feed liver water, lake water, water for agriculture or industrial discharge water which is water to be detected to a culture tank 1 as a culture medium and inoculate Chlorophyta into the culture tank 1, carry out culture and detect whether a harmful metal is contained in an amount of a prescribed value or above in water to be detected by extent of change in cell color of Chlorophyta in the culture medium. (2) This method for detecting a harmful metal is to carry out the method mentioned in the item (1) by previously obtaining the correlation between changing amount in cell color and harmful metal content and quantifying harmful metal in water to be detected.