A method of testing an analyzer utilizing a test piece that includes a first terminal portion (40A, 40B, 40C) and a second terminal portion (40D, 40E, 40F) for measuring a concentration of a specific component in a sample liquid supplied to the test piece, the analyzer comprising: a set portion in which the test piece is set; a first measurement terminal (P1, P3, P5) for electrical connection to the first terminal portion (40A, 40B, 40C); a second measurement terminal (P2, P4, P6) for electrical connection to the second terminal portion (40D, 40E, 40F); a measurement electrical circuit which measures voltages generated by the sample liquid in accordance with the concentration of the specific component; and a constant-voltage power supply that can change an output voltage level to one of a plurality of predefined trial voltages for checking working of the measurement electrical circuit; wherein the measurement electrical circuit is configured to measure a voltage of the first measurement terminal (P1, P3, P5); wherein the set portion is also configured to receive the check piece for conducting the checking of the working of the measurement electrical circuit; the method comprising: a preliminary step of setting a check piece instead of the test piece in the set portion to make an electrical path extending in the measurement electrical circuit and the check piece so that an output voltage level from the constant-voltage power supply can be conducted to at least one of the first measurement terminal (P1, P3, P5) and the second measurement terminal (P2, P4, P6), through the check piece and to the measurement electrical circuit; a first step for applying a trial voltage to the check piece; a second step for measuring a voltage response obtained from the measurement electrical circuit upon application of the trial voltage; and a third step for comparing the voltage response with an ideal voltage response; wherein the first through third steps are performed separately for each of the plurality of trial voltages. a set portion in which the test piece is set; a first measurement terminal (P1, P3, P5) for electrical connection to the first terminal portion (40A, 40B, 40C); a second measurement terminal (P2, P4, P6) for electrical connection to the second terminal portion (40D, 40E, 40F); a measurement electrical circuit which measures voltages generated by the sample liquid in accordance with the concentration of the specific component; and a constant-voltage power supply that can change an output voltage level to one of a plurality of predefined trial voltages for checking working of the measurement electrical circuit; wherein the measurement electrical circuit is configured to measure a voltage of the first measurement terminal (P1, P3, P5); wherein the set portion is also configured to receive the check piece for conducting the checking of the working of the measurement electrical circuit; the method comprising: a preliminary step of setting a check piece instead of the test piece in the set portion to make an electrical path extending in the measurement electrical circuit and the check piece so that an output voltage level from the constant-voltage power supply can be conducted to at least one of the first measurement terminal (P1, P3, P5) and the second measurement terminal (P2, P4, P6), through the check piece and to the measurement electrical circuit; a first step for applying a trial voltage to the check piece; a second step for measuring a voltage response obtained from the measurement electrical circuit upon application of the trial voltage; and a third step for comparing the voltage response with an ideal voltage response; wherein the first through third steps are performed separately for each of the plurality of trial voltages. a preliminary step of setting a check piece instead of the test piece in the set portion to make an electrical path extending in the measurement electrical circuit and the check piece so that an output voltage level from the constant-voltage power supply can be conducted to at least one of the first measurement terminal (P1, P3, P5) and the second measurement terminal (P2, P4, P6), through the check piece and to the measurement electrical circuit; a first step for applying a trial voltage to the check piece; a second step for measuring a voltage response obtained from the measurement electrical circuit upon application of the trial voltage; and a third step for comparing the voltage response with an ideal voltage response; wherein the first through third steps are performed separately for each of the plurality of trial voltages.