A biometric information detection device which is configured to be installed in an oral cavity, comprising: a sensor; a battery (6, 13); and a mechanical switch that switches between a conduction state in which power is supplied from the battery (6, 13) to the sensor and a cutoff state in which supply of the power is blocked, the biometric information detection device further comprising a sealing member that seals all of the sensor, the battery (6, 13), and the mechanical switch, and is configured to cover gums in the oral cavity; a holding member that is configured to cover teeth in the oral cavity and that is integrated with the sealing member; a strain sensor; and a signal processing unit that is sealed with the sealing member, is configured to receive supply of power from the battery (6, 13), and is configured to generate a data signal based on an output signal from the sensor, wherein the mechanical switch (12, 12A) includes an operation unit that is sealed with the sealing member (10B, 10C) and that is positioned so as to be supported by the gums when the biometric information detection device is installed in the oral cavity, the operation unit being configured to accept a pushing operation, the mechanical switch (12, 12A) is a self-holding type switch, the mechanical switch (12, 12A) further includes a main body, a first conductor and a second conductor, wherein the main body houses the first conductor and the second conductor, the operation unit is configured to perform a contact operation of bringing the first conductor into contact with the second conductor and a separation operation of separating the first conductor from the second conductor, and the strain sensor is connected to the battery (6, 13) through a power line and is connected to the signal processing unit through a communication line, the strain sensor being configured to receive supply of power from the battery and to transmit a detection signal to the signal processing unit, the device characterized in that the strain sensor is embedded in the holding member at a position configured to cover a crown part of the teeth when the biometric information detection device is installed in the oral cavity. a sensor; a battery (6, 13); and a mechanical switch that switches between a conduction state in which power is supplied from the battery (6, 13) to the sensor and a cutoff state in which supply of the power is blocked, the biometric information detection device further comprising a sealing member that seals all of the sensor, the battery (6, 13), and the mechanical switch, and is configured to cover gums in the oral cavity; a holding member that is configured to cover teeth in the oral cavity and that is integrated with the sealing member; a strain sensor; and a signal processing unit that is sealed with the sealing member, is configured to receive supply of power from the battery (6, 13), and is configured to generate a data signal based on an output signal from the sensor, wherein the mechanical switch (12, 12A) includes an operation unit that is sealed with the sealing member (10B, 10C) and that is positioned so as to be supported by the gums when the biometric information detection device is installed in the oral cavity, the operation unit being configured to accept a pushing operation, the mechanical switch (12, 12A) is a self-holding type switch, the mechanical switch (12, 12A) further includes a main body, a first conductor and a second conductor, wherein the main body houses the first conductor and the second conductor, the operation unit is configured to perform a contact operation of bringing the first conductor into contact with the second conductor and a separation operation of separating the first conductor from the second conductor, and the strain sensor is connected to the battery (6, 13) through a power line and is connected to the signal processing unit through a communication line, the strain sensor being configured to receive supply of power from the battery and to transmit a detection signal to the signal processing unit, the device characterized in that the strain sensor is embedded in the holding member at a position configured to cover a crown part of the teeth when the biometric information detection device is installed in the oral cavity.