A measuring device configured to measure a state of a solution, comprising: a measuring unit configured to output a measurement signal associated with the state of the solution; a protection unit attached to the measuring unit ; and a controller configured to obtain information on the state of the solution on the basis of the measurement signal output from the measuring unit , wherein the measuring unit has: a first part (P1) in a usable state that contributes to output of the measurement signal by coming into contact with the solution; and a second part (P2) that is isolated from the solution by the protection unit and is in a standby state for measurement, wherein: the information on the state of the solution includes a pH concentration; the measuring unit has a glass electrode unit , a first reference electrode unit and a second reference electrode unit used for glass electrode type pH measurement; the first part (P1) has a pair of the glass electrode unit and the first reference electrode unit ; and the second part (P2) has the second reference electrode unit characterized in that : the protection unit has a protection plate configured to isolate the second part (P2) of the measuring unit from the solution; and the protection plate is composed of at least one of biodegradable resin and acid-soluble resin. a measuring unit configured to output a measurement signal associated with the state of the solution; a protection unit attached to the measuring unit ; and a controller configured to obtain information on the state of the solution on the basis of the measurement signal output from the measuring unit , wherein the measuring unit has: a first part (P1) in a usable state that contributes to output of the measurement signal by coming into contact with the solution; and a second part (P2) that is isolated from the solution by the protection unit and is in a standby state for measurement, a first part (P1) in a usable state that contributes to output of the measurement signal by coming into contact with the solution; and a second part (P2) that is isolated from the solution by the protection unit and is in a standby state for measurement, wherein: the information on the state of the solution includes a pH concentration; the measuring unit has a glass electrode unit , a first reference electrode unit and a second reference electrode unit used for glass electrode type pH measurement; the first part (P1) has a pair of the glass electrode unit and the first reference electrode unit ; and the second part (P2) has the second reference electrode unit characterized in that : the protection unit has a protection plate configured to isolate the second part (P2) of the measuring unit from the solution; and the protection plate is composed of at least one of biodegradable resin and acid-soluble resin. the information on the state of the solution includes a pH concentration; the measuring unit has a glass electrode unit , a first reference electrode unit and a second reference electrode unit used for glass electrode type pH measurement; the first part (P1) has a pair of the glass electrode unit and the first reference electrode unit ; and the second part (P2) has the second reference electrode unit characterized in that : the protection unit has a protection plate configured to isolate the second part (P2) of the measuring unit from the solution; and the protection plate is composed of at least one of biodegradable resin and acid-soluble resin. the protection unit has a protection plate configured to isolate the second part (P2) of the measuring unit from the solution; and the protection plate is composed of at least one of biodegradable resin and acid-soluble resin. <EOS>