A pressure gauge comprising: a piston; a cylinder that has an internal space for slidably guiding the piston in a predetermined direction and has an opening for transmitting pressure from a target of which to measure pressure to the internal space; a stopper configured to restrict sliding of the piston in the internal space toward the opening to stop the piston at a predetermined position; a spring configured to bias the piston toward the opening and press the piston against the stopper; a first conversion mechanism (103L,102G) configured to convert a linear motion of the piston against an elastic force of the spring into a rotating motion about a first rotation shaft, the linear motion being caused by the pressure transmitted from the target to be measured to the internal space via the opening; an index that is fixed to one end side of the first rotation shaft; a dial configured to display a measurement value to be indicated by the index rotating about the first rotation shaft ' characterized in that the pressure gauge further comprises: momentum detecting means (102m,110) for detecting momentum indicating an amount of movement of the piston; a pressure sensor (Sp) configured to measure a pressure value of the pressure acting on the internal space of the cylinder; determining means for determining whether a difference between a first measurement value and a second measurement value exceeds a predetermined value, the first measurement value being estimated from the momentum detected by the momentum detecting means (102m,110) and indicated on the dial by the index, the second measurement value being measured by the pressure sensor (Sp); and notifying means for notifying a user if the determining means determines that the difference between the first measurement value and the second measurement value exceeds the predetermined value. a piston; a cylinder that has an internal space for slidably guiding the piston in a predetermined direction and has an opening for transmitting pressure from a target of which to measure pressure to the internal space; a stopper configured to restrict sliding of the piston in the internal space toward the opening to stop the piston at a predetermined position; a spring configured to bias the piston toward the opening and press the piston against the stopper; a first conversion mechanism (103L,102G) configured to convert a linear motion of the piston against an elastic force of the spring into a rotating motion about a first rotation shaft, the linear motion being caused by the pressure transmitted from the target to be measured to the internal space via the opening; an index that is fixed to one end side of the first rotation shaft; a dial configured to display a measurement value to be indicated by the index rotating about the first rotation shaft ' momentum detecting means (102m,110) for detecting momentum indicating an amount of movement of the piston; a pressure sensor (Sp) configured to measure a pressure value of the pressure acting on the internal space of the cylinder; determining means for determining whether a difference between a first measurement value and a second measurement value exceeds a predetermined value, the first measurement value being estimated from the momentum detected by the momentum detecting means (102m,110) and indicated on the dial by the index, the second measurement value being measured by the pressure sensor (Sp); and notifying means for notifying a user if the determining means determines that the difference between the first measurement value and the second measurement value exceeds the predetermined value.