To provide a remaining amount indicator device of a tank capable of correctly indicating a remaining amount of liquid in the tank on a indication means.

The remaining amount indicator device A of a tank including a control means H for indicating the remaining amount of the liquid for a detection value of a position detecting means 33 on the indication means 54 includes a controllable operation tool 56 which can be artificially operated. When the controllable operation tool 56 is operated while a predetermined amount L1 of the liquid is put in the tank 23, the control means H stores the detection value of the position detecting means 33 with the predetermined amount L1 of the liquid put as a reference value V1. A remaining amount L2 of the liquid for the detection value of the position detecting means 33 is indicated on the indication means 54 based on the stored reference value V1.