A medical instrument includes an insertion portion, first transmitting coils, second transmitting coils, a signal control unit, a position detection unit, a memory, and a position estimating unit. The signal control unit controls the first transmitting coils to transmit magnetic fields during a first predetermined period and controls the second transmitting coils to transmit magnetic fields during a second predetermined period. The position detection unit detects positions of the first transmitting coils during the first predetermined period and detects positions of the second transmitting coils during the second predetermined period. The memory stores the positions of the first transmitting coils. The position estimating unit estimates a shape of the insertion portion based on the positions of the second transmitting coils and the positions of the first transmitting coils stored in the memory.
