To provide an interface equipment at a low cost offering ease of maintenance.

When a transmission reception enable signal DTR (+5V-+15V) of positive logic is fed to a power terminal 20b of a constant voltage means 20 in the interface equipment 2, the constant voltage means 20 provides an output of a prescribed voltage as a power supply Vdd=3V. A protocol converter 23 or the like is energized by the power supply voltage Vdd. When a data signal TXD (H:+5V-+15V, L:-5V to -15V) is fed to a 1st level shift means 21, the 1st level shift means 21 provides an output of a data signal TXD that is level-shifted so as to be 3V at a high signal level and OV for a low signal level to the protocol converter 23. When the protocol converter 23 generates a transmission signal whose communication protocol is converted into a clock synchronization type, the transmission signal is outputted to a portable pulsation meter 1 via an input output means 24 of the portable equipment.