A reduction reverse gear for marine vessel comprising a hydraulic clutch-type forward/reverse rotation switching mechanism, wherein said forward/reverse rotation switching mechanism is configured to convert rotation power of a main engine mounted on a hull to an output of forward rotation, neutral, or reverse rotation and to transfer the output to a propeller, wherein neutral represents a state in which no rotation power is transmitted to the output, a forward/reverse rotation switching valve which is a three-position switching type including a forward rotation position, a neutral position and a reverse rotation position and is configured to control a switching operation of the forward/reverse rotation switching mechanism, and a trolling device configured to regulate and control the pressure of a working oil flowing toward the forward/reverse rotation switching mechanism, wherein the reduction reverse gear is configured such that: when the forward/reverse rotation switching valve is switched to the forward rotation position or the reverse rotation position during normal propulsion, wherein during normal propulsion the adjustment of the engine speed is made by means of a throttle lever, the trolling device is configured to control a pattern that reduces the pressure of the working oil flowing toward the forward/reverse rotation switching mechanism so that the pattern is different between when the forward/reverse rotation switching valve is in the forward rotation position and when the forward/reverse rotation switching valve is in the reverse rotation position; and the reduction reverse gear comprises an operation detection member configured to detect an operation state of the forward/reverse rotation switching valve; and when the operation detection member detects that the forward/reverse rotation switching valve is in the neutral position during normal propulsion, the trolling device is configured to control the working oil so that the pressure of the working oil flowing toward the forward/reverse rotation switching mechanism is not reduced. a hydraulic clutch-type forward/reverse rotation switching mechanism, wherein said forward/reverse rotation switching mechanism is configured to convert rotation power of a main engine mounted on a hull to an output of forward rotation, neutral, or reverse rotation and to transfer the output to a propeller, wherein neutral represents a state in which no rotation power is transmitted to the output, wherein said forward/reverse rotation switching mechanism is configured to convert rotation power of a main engine mounted on a hull to an output of forward rotation, neutral, or reverse rotation and to transfer the output to a propeller, wherein neutral represents a state in which no rotation power is transmitted to the output, a forward/reverse rotation switching valve which is a three-position switching type including a forward rotation position, a neutral position and a reverse rotation position and is configured to control a switching operation of the forward/reverse rotation switching mechanism, and a trolling device configured to regulate and control the pressure of a working oil flowing toward the forward/reverse rotation switching mechanism, wherein the reduction reverse gear is configured such that: when the forward/reverse rotation switching valve is switched to the forward rotation position or the reverse rotation position during normal propulsion, wherein during normal propulsion the adjustment of the engine speed is made by means of a throttle lever, the trolling device is configured to control a pattern that reduces the pressure of the working oil flowing toward the forward/reverse rotation switching mechanism so that the pattern is different between when the forward/reverse rotation switching valve is in the forward rotation position and when the forward/reverse rotation switching valve is in the reverse rotation position; and the reduction reverse gear comprises an operation detection member configured to detect an operation state of the forward/reverse rotation switching valve; and when the operation detection member detects that the forward/reverse rotation switching valve is in the neutral position during normal propulsion, the trolling device is configured to control the working oil so that the pressure of the working oil flowing toward the forward/reverse rotation switching mechanism is not reduced. when the forward/reverse rotation switching valve is switched to the forward rotation position or the reverse rotation position during normal propulsion, wherein during normal propulsion the adjustment of the engine speed is made by means of a throttle lever, the trolling device is configured to control a pattern that reduces the pressure of the working oil flowing toward the forward/reverse rotation switching mechanism so that the pattern is different between when the forward/reverse rotation switching valve is in the forward rotation position and when the forward/reverse rotation switching valve is in the reverse rotation position; and the reduction reverse gear comprises an operation detection member configured to detect an operation state of the forward/reverse rotation switching valve; and when the operation detection member detects that the forward/reverse rotation switching valve is in the neutral position during normal propulsion, the trolling device is configured to control the working oil so that the pressure of the working oil flowing toward the forward/reverse rotation switching mechanism is not reduced.