To provide a flasher display device of a two-frequency fish school detector for displaying a high-frequency display signal in a half part of a display plate and a low-frequency reflection signal in the other half part.

When a light-emitting body is detected by a first sensor 7a that is placed on the display plate of a display device 8, a high-frequency reflection wave signal is read from a first buffer function 19a that is incorporated into a control device 19 and is displayed at one half of the display device 8. Then, when the light-emitting body is detected by a second sensor 7b that is placed at a position opposite to the first sensor 7a of the display plate of the display device 8, a low-frequency reflection wave signal is conversely read and displayed by an inverse rotation reading function 19c from the second buffer function 19a that is incorporated in the control device 19, thus displaying a water surface at the upper portion of the display plate of the display device 8 and a school of fish and a water surface at the lower part, thus enabling the display to be seen easily and the difference in the reflection wave signals due to the difference in frequencies to be compared at a glance.