An apparatus which can solve the problem of participation of NO in hypotension in dialysis, hypoxia in dialysis, and the like during artificial dialysis by continuously monitoring fluctuation in a blood gas, an ionic component, or the like in body fluid such as blood and by suppressing these diseases, and quality evaluating means of an artificial dialyzer and dialyzing fluid are provided. An apparatus for an artificial kidney comprises a measurement monitor for continuously measuring nitric oxide as a component of body fluid or liquid for treatment. Further, an apparatus for an artificial kidney comprises a measurement monitor for measuring a component of body fluid or liquid for treatment, a display means for comparing a measurement measured by the measurement monitor with a control value, and when the measurement equals the control value, displays the equality, and oxygen supplying means.